aegis-authz-access-control

Scope & Objectives

Scan for authorization failures: code decides wrongly who may call an action (BFLA, vertical escalation) and which object instances an action may touch (BOLA/IDOR, horizontal escalation).

In scope:

• Missing or incorrect role/permission checks on routes, handlers, resolvers, controllers.
• Object fetches keyed by request-supplied IDs without ownership/tenant predicates.
• Multi-tenant isolation gaps (tenant context from input, shared caches/queues/indexes).
• Authorization logic bugs: deny-by-absence, OR-condition typos, verb tampering.
• Path normalization and proxy-header bypasses (X-Original-URL, X-Forwarded-For trust).
• Impersonation/API-key/service-trust features without scoping or audit.

Out of scope (other modules): authentication strength, session fixation, injection, SSRF, crypto. Only audit post-authentication decision logic here; flag unauthenticated reachability of privileged actions as BFLA.

Prerequisites & Vocabulary

Zero-background primer: the terms this module uses, one line each. Deeper plain-language explanations for every class live in the repository GUIDE.md glossary.

• BFLA: reaching an admin-only action because the route never checks your role
• BOLA / IDOR: changing an identifier in the request (order 1042 → 1043) to touch another user's object
• horizontal escalation: acting on someone else's data while staying at your own privilege level
• vertical escalation: doing things reserved for a higher role (ordinary user → admin)
• tenant: one customer's isolated slice of a shared multi-customer system
• deny-by-absence: when no explicit allow rule exists, the answer must be deny — a missing check is a finding, not "probably fine"
• taint flow / source→sink: path untrusted data travels from entry point to dangerous function
• finding status: Confirmed > Probable > Needs-Review; evidence rules in templates/finding-report.md

Mental Model

Evaluate every route along two independent axes; a route is safe only if BOTH pass.

Axis	Question	Failure	Primary CWE
Function (action)	May this subject invoke this endpoint at all?	BFLA / vertical escalation	CWE-862, CWE-863
Object (instance)	Given yes above, may it touch THIS row/file/tenant?	BOLA / IDOR / cross-tenant leak	CWE-639
Attribute	May it read/write THESE fields on the object?	Excessive data exposure, mass assignment	CWE-285

Decision procedure per route:

1. Identify the subject source: session, verified JWT sub claim, API key, mTLS identity. Anything else (query param, header like user_id, client-stored role) is a red flag by itself.
2. Identify required roles/actions from business naming (admin, /users, /internal, DELETE).
3. Locate where the object is fetched and whether the query embeds the subject (WHERE id = ? AND tenant_id = ?).
4. Locate the decision point (middleware/decorator/annotation/policy) and confirm it runs BEFORE any state change or data return.
5. Default answer when no explicit allow rule exists: deny. Absence of a check = finding, not "probably fine."

Two-account intuition: every endpoint must behave identically whether the caller owns the object or not — except for the owner, who alone gets data.

What To Check

Function-Level Authorization (BFLA)

• Enumerate every mutating route (POST/PUT/PATCH/DELETE) and every /admin, /internal, /manage subtree; verify each carries a guard that reads the server-side identity, not a client claim verbatim.
• Flag "security by obscurity": hidden UI buttons with no server check; SPA routes rendered only for admins while backing endpoints are open; endpoints whose only defense is an unguessable path segment.
• Check HTTP-method asymmetry: a controller guarded for GET but exposing DELETE/PATCH on the same path via a separate handler or catch-all (app.all('/admin/x', ...) without guard).
• Compare API versions: v1 module annotated/guarded, duplicated v2 controller forgotten. Diff guard counts per version directory.
• Test registration/update payloads for role mass assignment ("role":"admin", "isAdmin":true) accepted into the user record.
• Inspect debug/internal surfaces: Spring Actuator, Django admin + DEBUG views, Flask debugger, Go pprof, ASP.NET detailed errors, GraphQL introspection + mutations in production.

Object-Level Authorization (BOLA/IDOR)

• Trace each request parameter named id|uuid|guid|uid|email|slug|ref into the first DB/document lookup; require the predicate owner_id == subject.id or tenant_id == subject.tenant_id IN THE QUERY, not after it.
• Flag collection/list endpoints returning .all() / find() / Model.objects.all() serialized wholesale (mass listing leaks other tenants' rows).
• Nested resources: for /org/:orgId/doc/:docId, verify BOTH doc.orgId == orgId AND caller membership in orgId; membership check on the parent alone is insufficient.
• Export/report/download/CSV/PDF/streaming endpoints: these routinely skip guards because they bypass normal serializers. Grep for export|download|report|dump|backup|csv|xlsx.
• GraphQL: per-resolver object checks (not just a top-level auth directive), especially on nested fields (invoice.customer.address) and DataLoader/batch loaders that fetch by ID arrays.
• Sequential IDs (AutoField, serial, IDENTITY(1,1), incrementing numeric JSON ids): note as exploitability amplifier; UUIDs are mitigation only, never a substitute for predicates.
• Property-level granularity: field-level BOLA — record access correct but sensitive columns (salary, role, SSN-class fields) serialized to callers lacking need-to-know; diff serializer output per caller role.
• Mass assignment crossover: client-writable privileged fields ("role":"admin") are property-level authorization failure too; cross-ref the API module's mass-assignment class when spotted here.

Vertical & Horizontal Escalation

• Roles trusted from client storage: JWT claims (role, isAdmin, permissions) accepted without re-deriving from the authoritative store on sensitive calls; localStorage.getItem('role') gating UI-only.
• Forced browsing to admin panels: static admin bundles served publicly (express.static('admin')), framework admin at default paths with weak/no auth.
• Version-skew escalation: legacy /api/v1/admin/* kept alive after v2 hardening; old microservice copies of a moved endpoint still deployed.
• Cross-tenant context: tenant_id taken from request body/query/subdomain instead of the authenticated principal's record; Host-based tenancy spoofable via direct IP access or Host header override.
• Shared infrastructure keys: cache keys lacking tenant prefix (cache.get("invoice:"+id)), global search indexes, queue messages consumed without tenant re-check, temp files named by raw ID in shared dirs.

Logic, Header & Path Bypasses

• Allow vs deny style: find checks written as blocklists (if (role === 'banned') return) — invert them mentally; new roles inherit access silently.
• Boolean typos: role === 'admin' || userId === id granting admins everywhere is correct, but role !== 'admin' || userId !== id inside negations, or &&/|| swaps, produce accidental allows. Flag any compound condition mixing role equality and identity equality.
• Path normalization: routing decisions made on raw URLs before decode → %2f, //, /./, trailing dots, ;jsessionid, double encoding (%252f) splitting guard path from handler path.
• Verb tampering: guard attached per-method; try HEAD/OPTIONS/TRACE or method overrides (X-HTTP-Method-Override: DELETE, _method=DELETE form param).
• Proxy headers honored by app code: X-Original-URL, X-Rewrite-URL, X-Forwarded-Host, X-Forwarded-Proto used in routing/access decisions; X-Forwarded-For parsed for IP allowlists (req.headers['x-forwarded-for'].split(',')[0]) — spoofable unless app sits behind a trusted proxy configured to strip/set it.
• Framework-specific: ASP.NET [AllowAnonymous] on a controller overriding global fallback; Laravel $this->middleware() missing in constructor; Rails skip_before_action :authenticate_user!.

Delegation & Impersonation

• Support/admin impersonation ("login as customer"): verify scope limits (time-boxed, reason captured), immutable audit log entry with actor+target+reason, termination on password change, and no token minting that drops the original actor identity.
• API keys / PATs inheriting the full interactive-user permission set including admin roles; check key scopes exist and are enforced server-side.
• Service-to-service: internal endpoints trusting a forwarded username/email header set by "some gateway" (X-User-Email) with no signature verification; mTLS absent on internal hops assumed.
• OAuth token exchange: scope downgrades ignored; refresh tokens carrying original broad scopes after admin revocation.

Where To Look

Stack	Route table	Guard markers (present = good)	Files/dirs
Express/Fastify/NestJS	app.use/router.stack, Nest @Controller metadata, Fastify printRoutes	requireAuth, passport.authenticate, addHook('preHandler'), @UseGuards(...), @Roles(...)	routes/, controllers/, *.controller.ts, main.ts
Django/DRF	urls.py, router.register, django-extensions show_urls	LoginRequiredMixin, PermissionRequiredMixin, permission_classes, DRF get_queryset filter	*/urls.py, views.py, viewsets.py, serializers.py
Flask/FastAPI	decorators @app.route/@get/@post, OpenAPI spec	before_request, @login_required, `Depends(current_user	require_roles), router-level dependencies=[...]`
Spring (Java/Kotlin)	@RequestMapping tree, Actuator /mappings (guarded!)	@PreAuthorize, @Secured, @RolesAllowed, SecurityFilterChain matchers, @EnableMethodSecurity	**/controller/**, SecurityConfig.*, application.yml
ASP.NET Core	Controllers + minimal-API Map* chain	[Authorize], [Authorize(Policy=...)], .RequireAuthorization(), FallbackPolicy, [AllowAnonymous] (audit each)	Controllers/, Program.cs, Startup.cs
Laravel/Symfony	php artisan route:list, bin/console debug:router	auth: middleware, can: middleware, policies, Gate::authorize, Symfony voters + access_control YAML	routes/web.php, routes/api.php, app/Policies, config/packages/security.yaml
Rails	rails routes	before_action :authenticate_user!, Pundit authorize @record / after_action :verify_authorized, CanCanCan load_and_authorize_resource	config/routes.rb, app/controllers/**, app/policies/**
Go (net/http/chi/gin)	mux registrations, chi walk	middleware wrappers RequireAuth/RequireRole, gin.Use(...), group-scoped r.Group(func(r){ r.Use(guard)})	cmd/*/main.go, internal/http/**, middleware/

Also inspect: docker-compose.yml/k8s manifests for internal-only ports (context, not proof), OpenAPI/Swagger specs vs implemented routes (spec drift = undocumented live routes), seeders/fixtures revealing role names, frontend JS bundles for hidden admin routes (/static/js/*.js contains "/admin" strings).

Patterns & Signatures

Route inventory (run first; diff counts against guard markers):

rg -n "@(Get|Post|Put|Patch|Delete|Request)Mapping\(" --type java --type kt
rg -n "@app\.(route|get|post|put|patch|delete)|@(get|post|put|delete)\(" --type py
rg -n "\.(get|post|put|patch|delete|all)\(\s*['\"][^'\"]+" -t ts -t js
rg -n "Route::(get|post|put|patch|delete|any|resource|apiResource)" --type php
rg -n "(map|Map)(Get|Post|Put|Delete|Patch)\(\"" --type cs
rg -n "HandleFunc|\.GET\(|\.POST\(|\.DELETE\(|\.PUT\(" --type go

Guard-presence markers:

@(PreAuthorize|Secured|RolesAllowed|PostAuthorize)\(

(LoginRequiredMixin|PermissionRequiredMixin|UserPassesTestMixin)

(@UseGuards|@Roles\(|SetMetadata\(['"](roles|permissions))

Missing-guard smell (Express: handler as 2nd arg, no middleware between):

\.(get|post|put|patch|delete)\(\s*['"][^'"]*['"]\s*,\s*(async\s*)?\(?[A-Za-z_$]

Object-fetch-without-subject heuristics:

objects\.(get|filter)\((pk|id)=

findById\((req|params|pathVariable)[^)]*\)

Model\.objects\.all\(\)

Client-trusted identity signals:

(decoded|payload|claims|token)\.(role|isAdmin|is_admin|admin|permissions)

localStorage\.(getItem\(['"]?(role|is_admin|isAdmin|user)['"]?\))

(req\.body|request\.body|payload)\.(role|isAdmin|is_admin|account_type)

Header/path bypass primitives:

(?i)x-(original-url|rewrite-url|forwarded-for|forwarded-host|http-method-override)

headers\[['"](x-forwarded-for|x-real-ip)['"]\]

(_method|X-HTTP-Method-Override|method_override)

Impersonation & delegation:

(impersonat(e|ion)|acting_as|act_as|as_user|become_user|sudo_mode)

(api[_-]?key|personal_access_token).{0,40}(scopes?|abilities?)

Debug/internal exposure:

(/debug/pprof|/actuator|/_profiler|/__profiler|/telescope|/horizon|DEBUG\s*=\s*True)

Tenant-context-from-input:

(tenant_id|org_id|organization_id)['"]?\s*[:=]\s*(req\.(query|params|body)|request\.(GET|data|json))

Taint Tracing Guidance

Sources (untrusted until proven otherwise): all route params, query strings, bodies, JWT payload claims other than the verified sub, headers (X-*, even Authorization API keys), subdomain/Host, message-queue payloads.

Sinks (authorization-relevant): ORM/document queries (findOne/findById/get/filter/Query.first), raw SQL, file reads/writes/downloads, cache get/put, queue publish/consume, admin RPC calls, email/export generation containing other users' data.

Procedure:

1. For each sink fetching a singleton, list its arguments. Flag any lookup helper whose signature lacks a user/tenant/principal parameter — e.g., getInvoice(id) vs getInvoice(id, actor); the omission predicts BOLA upstream of any later check.
2. Walk backward from sink to source: if the predicate chain from param → WHERE clause does not include the authenticated principal attribute, mark BOLA candidate.
3. Track role/permission values: if the value used in the decision originates from a source (JWT body, DB column writable via profile update, Redis session field set from login-time client data) rather than the canonical user store, mark escalation candidate.
4. For caches/queues, trace key construction and consumer-side filtering; a tenant tag on write but no filter on read is still vulnerable.
5. Sanitizers do NOT exist for authz — a validated integer ID is still a valid other-tenant ID. Never treat validation as authorization.

Framework shortcuts: DRF get_queryset() overrides (absence = base manager queryset = leak); Rails ApplicationRecord default scopes (none by default); SQLAlchemy session.query(Model).get(id) ignores any Python-level tenant notion unless filters added; JPA EntityManager.find(Cls, id) never tenant-filters without Hibernate @TenantId/@Filter.

Exploitation & Reproduction

Two-Account BOLA Test (canonical sequence)

1. Register victim and attacker accounts:

   curl -s -X POST https://target/api/register -H 'Content-Type: application/json' \
     -d '{"email":"[email protected]","password":"V1ctimPass!"}'
   curl -s -X POST https://target/api/register -H 'Content-Type: application/json' \
     -d '{"email":"[email protected]","password":"Att4ckerPass!"}'
   

2. Authenticate both; store tokens:

   VICTIM=$(curl -s -X POST https://target/api/login -H 'Content-Type: application/json' \
     -d '{"email":"[email protected]","password":"V1ctimPass!"}' | jq -r .token)
   ATTACKER=$(curl -s -X POST https://target/api/login -H 'Content-Type: application/json' \
     -d '{"email":"[email protected]","password":"Att4ckerPass!"}' | jq -r .token)
   

3. Victim creates an object; capture its ID:

   curl -s -X POST https://target/api/invoices -H "Authorization: Bearer $VICTIM" \
     -H 'Content-Type: application/json' -d '{"amount":100,"memo":"secret-payroll"}'
   # -> {"id":1042,...}   (sequential => enumerate 1030..1050 next)
   

4. Attacker requests the victim's object:

   curl -i https://target/api/invoices/1042 -H "Authorization: Bearer $ATTACKER"
   

5. Interpret (this triage matters):

   Result	Meaning
   200 + victim's fields ("secret-payroll")	Confirmed BOLA (CWE-639)
   200 + empty/redacted body but different timing than random IDs	Existence oracle; partial protection
   403	Function reachable, object denied — check OTHER verbs (curl -i -X PUT/PATCH/DELETE) and nested paths before clearing
   404 for foreign IDs, 200 for own	Correct anti-enumeration masking — verify owner still receives full record

6. Repeat for write paths (swap IDs on PATCH/DELETE), collections (GET /api/invoices without ?mine=1), exports (GET /api/invoices/export.csv), and nested forms (GET /org/A/invoices/1042 where 1042 belongs to org B).
7. Static-only confirmation (no test accounts available): locate the handler for the route, show the fetch statement has no ownership predicate, and show no policy/middleware wraps the route — cite file:line for both halves.

BFLA Admin-Endpoint Test

1. As ATTACKER (normal user), call an administrative mutation:

   curl -i -X POST https://target/api/users -H "Authorization: Bearer $ATTACKER" \
     -H 'Content-Type: application/json' -d '{"email":"[email protected]","password":"Pwn3dPass!","role":"admin"}'
   

2. Outcomes: 201/200 = confirmed BFLA (+ possible privilege self-grant); 403 = guarded; 401 = route also misses authentication (worse).
3. Role-injection variant at registration/update:

   curl -s -o /dev/null -w '%{http_code}\n' -X POST https://target/api/register \
     -H 'Content-Type: application/json' \
     -d '{"email":"[email protected]","password":"Esc4late!","role":"admin","isAdmin":true}'
   # then re-login as [email protected] and retry step 1
   

4. Method-swap variant against GET-guarded routes: curl -i -X DELETE https://target/admin/users/42 -H "Authorization: Bearer $ATTACKER".

Path/Header/Verb Bypass Tests

# Path confusion (use --path-as-is so curl does not normalize)
for p in '/admin/users' '/admin//users' '/admin/./users' '/admin%2fusers' '/adm%69n/users' \
         '/admin;/users' '/admin/users/' '/ADMIN/users' '/api/v1/admin/stats'; do
  curl -s -o /dev/null -w "%{http_code} $p\n" --path-as-is "https://target$p" -H "Authorization: Bearer $ATTACKER"
done
# Double-encoding round trip: %252f decodes once to %2f, again to '/'
# Proxy-header injection
curl -s -o /dev/null -w '%{http_code}\n' 'https://target/public/health' -H 'X-Original-URL: /admin/users'
curl -s -o /dev/null -w '%{http_code}\n' 'https://target/admin/stats'  -H 'X-Forwarded-For: 10.0.0.1'
# Verb tampering incl. overrides
for m in HEAD OPTIONS TRACE PATCH PUT; do curl -s -o /dev/null -w "%{http_code} $m\n" -X $m https://target/api/invoices/1042 -H "Authorization: Bearer $ATTACKER"; done
curl -s -X POST https://target/api/invoices/1042 -H "Authorization: Bearer $ATTACKER" \
  -H 'X-HTTP-Method-Override: DELETE' -d '_method=DELETE'

Expected observable outcome: any status other than uniform 403/404 across all variants (and identical behavior with a valid-but-unprivileged token) demonstrates a guard-bypass primitive; record which exact byte-sequence bypassed it.

Remediation

Centralize the Policy Layer

Move every decision into ONE choke point per stack; handlers may refine but never be the sole guard:

Stack	Choke point
Express/Fastify	Router-level middleware registered before branch handlers (guardRouter.use(requireAuth, attachPolicy))
NestJS	Global APP_GUARD JwtAuthGuard + RolesGuard; per-handler @Roles() metadata
FastAPI	dependencies=[Depends(require_auth)] on the router; policy dependency per operation
Django	Mixins on every CBV + DRF DEFAULT_PERMISSION_CLASSES + custom get_queryset base class
Flask	before_request blueprint hook + decorator on every view
Spring	SecurityFilterChain path rules + @EnableMethodSecurity + @PreAuthorize default-deny meta-annotation
ASP.NET Core	FallbackPolicy = RequireAuthenticatedUser globally; [Authorize(Policy)] per area
Laravel	Route middleware groups (auth:sanctum) + Policies auto-discovery; $gate->deny default
Symfony	access_control YAML + voters invoked via isGranted in a base controller/subscriber
Rails	before_action :authenticate_user! in ApplicationController + Pundit verify_authorized after_action raising on skipped checks
Go	Single func Authz(next http.Handler) http.Handler wrapper composed onto every non-public route group

Before / After Recipes

Express:

// VULNERABLE
router.get('/invoices/:id', async (req, res) => {
  const inv = await Invoice.findByPk(req.params.id);
  res.json(inv);
});

// FIXED
const { requireAuth } = require('./middleware/auth');
const { authorize } = require('./policy');            // centralized decision engine
const { scopeToTenant } = require('./middleware/tenant');

router.get('/invoices/:id', requireAuth, authorize('invoice:read'),
  scopeToTenant, async (req, res) => {
    const inv = await Invoice.findOne({               // predicate lives IN the query
      where: { id: req.params.id, tenantId: req.user.tenantId }
    });
    if (!inv) return res.sendStatus(404);             // uniform mask, no existence oracle
    res.json(inv);
  });

Django/DRF:

# VULNERABLE
class InvoiceViewSet(viewsets.ModelViewSet):
    queryset = Invoice.objects.all()
    serializer_class = InvoiceSerializer

# FIXED
class InvoiceViewSet(viewsets.ModelViewSet):
    serializer_class = InvoiceSerializer
    permission_classes = [IsAuthenticated, TenantMemberRequired]

    def get_queryset(self):                            # object axis enforced centrally
        return Invoice.objects.filter(
            tenant_id=self.request.user.tenant_id,
        )

# FIXED (classic Django CBV equivalent)
class InvoiceDetailView(LoginRequiredMixin, PermissionRequiredMixin, DetailView):
    model = Invoice
    permission_required = 'invoices.view_invoice'

    def get_queryset(self):
        return Invoice.objects.filter(tenant=self.request.user.tenant)

Spring:

// VULNERABLE
@GetMapping("/api/v2/invoices/{id}")
public InvoiceDto get(@PathVariable long id) {
    return invoices.findById(id).map(mapper::toDto)
        .orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND));
}

// FIXED
@PreAuthorize("hasAuthority('invoice:read')")
@GetMapping("/api/v2/invoices/{id}")
public InvoiceDto get(@PathVariable long id, @AuthenticationPrincipal AppUser user) {
    return invoices.findByIdAndTenantId(id, user.getTenantId())
        .map(mapper::toDto)
        .orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND));
}

Laravel:

// VULNERABLE
Route::get('/invoices/{invoice}', [InvoiceController::class, 'show']);

// FIXED
Route::middleware(['auth:sanctum'])
    ->get('/invoices/{invoice}', [InvoiceController::class, 'show'])
    ->middleware('can:view,invoice');                 // policy = single decision point

// app/Policies/InvoicePolicy.php  (registered automatically by name convention)
class InvoicePolicy
{
    public function view(User $user, Invoice $invoice): bool
    {
        return $user->tenant_id === $invoice->tenant_id;
    }
}

Rails (Pundit):

# VULNERABLE
def show
  @invoice = Invoice.find(params[:id])
end

# FIXED
def show
  @invoice = Invoice.find(params[:id])
  authorize @invoice                                   # raises unless policy permits
end
# with_scope in policy keeps index endpoints tenant-safe:
class ApplicationPolicy
  class Scope
    def resolve
      scope.where(tenant_id: user.tenant_id)
    end
  end
end

Deny-by-Default Routing

// Express: public surface is an EXPLICIT allowlist; everything else falls through the guard wall
app.use(['/health', '/live', '/ready', '/login', '/register'], publicRouter);
app.use(requireAuth);                       // wall: nothing below resolves without identity
app.use('/admin', requireRole('admin'));    // vertical wall for whole subtree
app.use('/api', apiRouter);                 // apiRouter assumes authenticated ctx

# Spring Security: authenticate everything, permit only listed public paths
security:
  config:
    http:
      authorizeHttpRequests:
        - "/health"
        - "/login"
      others: "authenticated"
      admin-prefix: "/admin/**"
      admin-role: "ROLE_ADMIN"
    method-security: true

Equivalent defaults: ASP.NET FallbackPolicy (see below), Symfony last-resort - { path: ^/, roles: ROLE_USER }, Laravel auth on the api group, Rails authenticate in ApplicationController with skip_before_action audited per use.

// ASP.NET Core: fail closed
builder.Services.AddAuthorization(o =>
{
    o.FallbackPolicy = new AuthorizationPolicyBuilder()
        .RequireAuthenticatedUser().Build();
});
// minimal APIs: app.MapGet("/x", h).RequireAuthorization("TenantMember");

Tenant Scoping & Row-Level Security

• Enforce tenancy in ONE layer beneath all queries: repository base classes, DRF get_queryset, EF Core global query filters (HasQueryFilter(i => i.TenantId == _tenant.Id)), Hibernate @Filter/@TenantId, SQLAlchemy events, or Postgres RLS as backstop:

-- Postgres row-level security as defense-in-depth under app-level checks
ALTER TABLE invoices ENABLE ROW LEVEL SECURITY;
CREATE POLICY tenant_isolation ON invoices
  USING (tenant_id = current_setting('app.tenant_id')::uuid);
-- per request/connection: SET LOCAL app.tenant_id = '<uuid-from-session>';

• Name cache keys and queue headers with tenant scope (t:{tenant}:invoice:{id}); re-validate tenant on consume.
• Replace sequential integers with opaque UUIDv4 for external references (mitigation, not fix).
• Impersonation: dedicated short-TTL token type carrying act (actor) + target, reason string persisted to append-only audit table, auto-expiry on target password change, admin-only grant of the impersonation permission itself.

Verification & Validation

Automated Tests (GIVEN/WHEN/THEN)

Scenario: Owner retains access (negative test against over-blocking)
  GIVEN user A authenticated and owning invoice 1042
  WHEN A requests GET /api/invoices/1042
  THEN status is 200 AND body contains A's memo value

Scenario: Non-owner denied on read
  GIVEN users A and B on distinct tenants
  WHEN B requests GET /api/invoices/1042
  THEN status is 403 or 404 AND body contains no A-owned field values

Scenario: Non-owner denied on write
  WHEN B sends PATCH /api/invoices/1042 {"amount": 1}
  THEN status is 403/404 AND a follow-up GET by A shows unchanged amount

Scenario: Role matrix cell denial
  GIVEN role "viewer" exists with read-only rights
  WHEN viewer calls DELETE /api/invoices/1042
  THEN status is 403 regardless of ownership

Scenario: Unauthenticated denial
  WHEN request omits credentials entirely
  THEN status is 401 for every non-public route

Run the matrix for EVERY route × EVERY role × {own, foreign, nonexistent} object ID; assert status codes, not just absence of error text.

Route-Coverage Test (deny-by-default assertion)

// pseudocode — port enumerator per framework (Express stack walk, rails routes, artisan route:list)
const PUBLIC_ROUTES = new Set(['/health', '/live', '/ready', '/login', '/register', '/docs', '/openapi.json']);

test('every non-public route declares >=1 authz guard; no public mutations', () => {
  for (const r of enumerateRoutes(app)) {
    const isPublic = PUBLIC_ROUTES.has(r.path);
    const guards = r.middleware.filter(isAuthzGuard); // requireAuth/authorize/roles...
    expect(guards.length >= 1 || isPublic).toBe(true);           // deny-by-default
    if (isPublic) expect(r.methods.some(m => ['POST','PUT','PATCH','DELETE'].includes(m))).toBe(false);
  }
});

CI companion: snapshot-test the route table (rails routes, artisan route:list, Nest route dump) and fail review when count grows without a paired guard change.

Manual Re-test Checklist

1. Re-run two-account sequence from Exploitation section; confirm 403/404 and owner 200.
2. Re-run all path/header/verb bypass loops; confirm uniform denial.
3. Confirm admin can STILL operate (fixes frequently over-block; test each role-matrix cell positively).
4. Confirm export/download and GraphQL nested-field paths now enforce ownership.
5. Confirm impersonation writes audit rows and expires correctly.
6. Confirm cache keys are tenant-prefixed and stale pre-fix entries purged (flush affected namespaces).

Post-Fix Greps

rg -n "skip_authorization|SkipAuthorization" app/
rg -n "objects\.(get|filter)\((pk|id)=" --type py
rg -n "findById\(" --type java --type kt | rg -v "AndTenant|ForTenant|Scoped"
rg -ni "x-(original-url|rewrite-url)" .
rg -n "x-forwarded-for" -i . | rg -v "trust proxy|trustedProxies|rate.?limit"
rg -n "@(Get|Post|Put|Delete|Patch)Mapping\(" --type java --type kt | wc -l   # compare vs @PreAuthorize count

Severity Assessment

Finding archetype	Example	Baseline CVSS v3.1 vector	Score band
Unauthenticated admin action	POST /api/users reachable pre-auth	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H	Critical (9.8)
Vertical escalation, authenticated write	normal user creates/disables users	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H	High (8.8)
Cross-tenant bulk read	listing returns all tenants' records (scope-changing)	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N	High (7.7)
Horizontal write, single object	attacker edits another tenant's invoice	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N	Medium–High (6.5)
Single-record cross-tenant read	one foreign record via guessed ID, high-sensitivity data	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N	Medium (6.5)
Existence/timing oracle only	200-empty vs 404 differentiation	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N	Low–Medium (3.1–4.3)

Rubric modifiers: enumerable sequential IDs or absent rate limits push one band up; secrets/PHI/financial fields push up; compensating network ACLs on genuinely internal-only services push down but never to informational while the code defect persists. Admin takeover ≥9.0 always Critical; cross-tenant read defaults High even for one record when data is personal or confidential.

Primary CWE mapping: missing guard entirely → CWE-862; guard present but wrong → CWE-863; user-controlled key to another's object → CWE-639; umbrella → CWE-285; shared cache/queue granularity → CWE-1220.

Common False Positives

• Gateway/sidecar enforcement: bare handlers behind an authorizing API gateway, service mesh AuthorizationPolicy, or mTLS-spiffe mesh. Verify the enforcement point exists and covers the route before dismissing; document it in the report.
• Intentionally public endpoints: pricing catalogs, status pages, docs — confirm product intent and absence of mutation methods.
• UUID capability references: unguessable IDs reduce practical exploitability, but the missing ownership predicate remains a real defect — report as lower-severity hardening gap, not a false positive of the pattern itself.
• Deliberate 404-masking: uniform 404 for foreign objects with 200 for owners is correct design, not a leak — confirm response timing/body are indistinguishable for nonexistent vs foreign IDs.
• Dev/test-only routes compiled out of production builds (verify build flags/env gates actually exclude them, e.g., if (process.env.NODE_ENV !== 'production')).
• Internal tools behind VPN + mTLS where identity is established at network layer — residual risk note only if the same service also binds a public interface.
• Read endpoints already filtered at the serializer to public fields — confirm no private field slips through relations/nested serializers.

References

• CWE-284: Improper Access Control
• CWE-285: Improper Authorization
• CWE-639: Authorization Bypass Through User-Controlled Key
• CWE-862: Missing Authorization
• CWE-863: Incorrect Authorization
• CWE-1220: Insufficient Resource Granularity
• OWASP Cheat Sheet Series: Authorization Cheat Sheet
• OWASP Cheat Sheet Series: Access Control Cheat Sheet
• OWASP Cheat Sheet Series: Insecure Direct Object Reference Prevention Cheat Sheet
• OWASP API Security Top 10 (2023): API1 Broken Object Level Authorization
• OWASP API Security Top 10 (2023): API5 Broken Function Level Authorization
• OWASP Top 10 (2021): A01 Broken Access Control
• OWASP ASVS 4.0.x — Section V4 Access Control