analyzing-cobalt-strike-beacon-configuration

分析 Cobalt Strike Beacon 配置

概述

Cobalt Strike 是一款商业化对手模拟工具，常被威胁行为者滥用于后渗透行动。Beacon 载荷中嵌入的配置数据会揭示 C2 服务地址、通信协议、休眠间隔、抖动值、可塑性 C2 配置文件设置、水印标识符和加密密钥。从 PE 文件、Shellcode 或内存转储中提取这些配置，对于事件响应人员绘制攻击者基础设施并归因攻击活动至关重要。Beacon 配置使用单字节（版本 3 为 0x69，版本 4 为 0x2e）进行 XOR 编码，并以类型-长度-值（TLV）格式存储在 .data 节中。

适用场景

• 调查需要分析 Cobalt Strike Beacon 配置的安全事件时
• 为此领域构建检测规则或威胁狩猎查询时
• SOC 分析师需要此类分析的结构化流程时
• 验证针对相关攻击技术的安全监控覆盖情况时

前提条件

• Python 3.9+，以及 dissect.cobaltstrike、pefile、yara-python
• SentinelOne CobaltStrikeParser（parse_beacon_config.py）
• 用于手动检查的十六进制编辑器（010 Editor、HxD）
• 了解 PE 文件格式和 XOR 编码
• 内存转储采集工具（Volatility3、WinDbg）
• 用于关联 C2 流量的网络分析工具（Wireshark）

关键概念

Beacon 配置结构

Cobalt Strike Beacon 会将配置存储为 TLV（类型-长度-值）条目组成的数据块，位于 PE 的 .data 节中。无阶段 Beacon 会使用 4 字节密钥对整个 Beacon 代码进行 XOR 运算。配置数据块本身使用单字节 XOR 密钥。每个 TLV 条目包含一个 2 字节类型标识符（例如，BeaconType 为 0x0001，C2Server 为 0x0008）、一个 2 字节长度字段和长度可变的数据。

可塑性 C2 配置文件

Beacon 配置中编码了可塑性 C2 配置文件，用于规定 HTTP 请求/响应转换方式，包括 URI 路径、标头、元数据编码（Base64、NetBIOS）和数据转换。分析这些设置可以揭示 Beacon 如何伪装流量，使其融入合法的 Web 流量。

水印与许可证识别

每个 Cobalt Strike 许可证都会在生成的 Beacon 中嵌入一个唯一水印（4 字节整数）。提取水印可以将多个 Beacon 关联到同一操作人员或破解的许可证。威胁情报提供商维护的已知水印数据库，可将水印映射到特定威胁行为者或泄露的许可证密钥。

工作流

步骤 1：使用 CobaltStrikeParser 提取配置

#!/usr/bin/env python3
"""Extract Cobalt Strike beacon config from PE or memory dump."""
import sys
import json

# Using SentinelOne's CobaltStrikeParser
# pip install dissect.cobaltstrike
from dissect.cobaltstrike.beacon import BeaconConfig

def extract_beacon_config(filepath):
    """Parse beacon configuration from file."""
    configs = list(BeaconConfig.from_path(filepath))

    if not configs:
        print(f"[-] No beacon configuration found in {filepath}")
        return None

    for i, config in enumerate(configs):
        print(f"\n[+] Beacon Configuration #{i+1}")
        print(f"{'='*60}")

        settings = config.as_dict()

        # Critical fields for incident response
        critical_fields = [
            "SETTING_C2_REQUEST",
            "SETTING_C2_RECOVER",
            "SETTING_PUBKEY",
            "SETTING_DOMAINS",
            "SETTING_BEACONTYPE",
            "SETTING_PORT",
            "SETTING_SLEEPTIME",
            "SETTING_JITTER",
            "SETTING_MAXGET",
            "SETTING_SPAWNTO_X86",
            "SETTING_SPAWNTO_X64",
            "SETTING_PIPENAME",
            "SETTING_WATERMARK",
            "SETTING_C2_VERB_GET",
            "SETTING_C2_VERB_POST",
            "SETTING_USERAGENT",
            "SETTING_PROTOCOL",
        ]

        for field in critical_fields:
            value = settings.get(field, "N/A")
            print(f"  {field}: {value}")

        return settings

    return None


def extract_c2_indicators(config):
    """Extract actionable C2 indicators from beacon config."""
    indicators = {
        "c2_domains": [],
        "c2_ips": [],
        "c2_urls": [],
        "user_agent": "",
        "named_pipes": [],
        "spawn_processes": [],
        "watermark": "",
    }

    if not config:
        return indicators

    # Extract C2 domains
    domains = config.get("SETTING_DOMAINS", "")
    if domains:
        for domain in str(domains).split(","):
            domain = domain.strip().rstrip("/")
            if domain:
                indicators["c2_domains"].append(domain)

    # Extract user agent
    indicators["user_agent"] = str(config.get("SETTING_USERAGENT", ""))

    # Extract named pipes
    pipe = config.get("SETTING_PIPENAME", "")
    if pipe:
        indicators["named_pipes"].append(str(pipe))

    # Extract spawn-to processes
    for arch in ["SETTING_SPAWNTO_X86", "SETTING_SPAWNTO_X64"]:
        proc = config.get(arch, "")
        if proc:
            indicators["spawn_processes"].append(str(proc))

    # Extract watermark
    indicators["watermark"] = str(config.get("SETTING_WATERMARK", ""))

    return indicators


if __name__ == "__main__":
    if len(sys.argv) < 2:
        print(f"Usage: {sys.argv[0]} <beacon_file_or_dump>")
        sys.exit(1)

    config = extract_beacon_config(sys.argv[1])
    if config:
        indicators = extract_c2_indicators(config)
        print(f"\n[+] Extracted C2 Indicators:")
        print(json.dumps(indicators, indent=2))

步骤 2：手动 XOR 解密 Beacon 配置

import struct

def find_and_decrypt_config(data):
    """Manually locate and decrypt beacon configuration."""
    # Cobalt Strike 4.x uses 0x2e as XOR key
    xor_keys = [0x2e, 0x69]  # v4, v3

    for xor_key in xor_keys:
        # Search for the config magic bytes after XOR
        # Config starts with 0x0001 (BeaconType) XOR'd with key
        magic = bytes([0x00 ^ xor_key, 0x01 ^ xor_key,
                       0x00 ^ xor_key, 0x02 ^ xor_key])

        offset = data.find(magic)
        if offset == -1:
            continue

        print(f"[+] Found config at offset 0x{offset:x} (XOR key: 0x{xor_key:02x})")

        # Decrypt the config blob (typically 4096 bytes)
        config_size = 4096
        encrypted = data[offset:offset + config_size]
        decrypted = bytes([b ^ xor_key for b in encrypted])

        # Parse TLV entries
        entries = parse_tlv(decrypted)
        return entries

    return None


def parse_tlv(data):
    """Parse Type-Length-Value configuration entries."""
    entries = {}
    offset = 0

    # TLV field type mapping
    field_names = {
        0x0001: "BeaconType",
        0x0002: "Port",
        0x0003: "SleepTime",
        0x0004: "MaxGetSize",
        0x0005: "Jitter",
        0x0006: "MaxDNS",
        0x0007: "Deprecated_PublicKey",
        0x0008: "C2Server",
        0x0009: "UserAgent",
        0x000a: "PostURI",
        0x000b: "Malleable_C2_Instructions",
        0x000c: "Deprecated_HttpGet_Metadata",
        0x000d: "SpawnTo_x86",
        0x000e: "SpawnTo_x64",
        0x000f: "CryptoScheme",
        0x001a: "Watermark",
        0x001d: "C2_HostHeader",
        0x0024: "PipeName",
        0x0025: "Year",
        0x0026: "Month",
        0x0027: "Day",
        0x0036: "ProxyHostname",
    }

    while offset + 6 <= len(data):
        entry_type = struct.unpack(">H", data[offset:offset+2])[0]
        entry_len_type = struct.unpack(">H", data[offset+2:offset+4])[0]
        entry_len = struct.unpack(">H", data[offset+4:offset+6])[0]

        if entry_type == 0:
            break

        value_start = offset + 6
        value_end = value_start + entry_len
        value_data = data[value_start:value_end]

        field_name = field_names.get(entry_type, f"Unknown_0x{entry_type:04x}")

        if entry_len_type == 1:  # Short
            value = struct.unpack(">H", value_data[:2])[0]
        elif entry_len_type == 2:  # Int
            value = struct.unpack(">I", value_data[:4])[0]
        elif entry_len_type == 3:  # String/Blob
            value = value_data.rstrip(b'\x00').decode('utf-8', errors='replace')
        else:
            value = value_data.hex()

        entries[field_name] = value
        print(f"  {field_name}: {value}")

        offset = value_end

    return entries

步骤 3：用于检测 Beacon 的 YARA 规则

import yara

cobalt_strike_rule = """
rule CobaltStrike_Beacon_Config {
    meta:
        description = "Detects Cobalt Strike beacon configuration"
        author = "Malware Analysis Team"
        date = "2025-01-01"

    strings:
        // XOR'd config marker for CS 4.x (key 0x2e)
        $config_v4 = { 2e 2f 2e 2c }

        // XOR'd config marker for CS 3.x (key 0x69)
        $config_v3 = { 69 68 69 6b }

        // Common beacon strings
        $str_pipe = "\\\\.\\pipe\\" ascii wide
        $str_beacon = "beacon" ascii nocase
        $str_sleeptime = "sleeptime" ascii nocase

        // Reflective loader pattern
        $reflective = { 4D 5A 41 52 55 48 89 E5 }

    condition:
        ($config_v4 or $config_v3) or
        (2 of ($str_*) and $reflective)
}
"""

def scan_for_beacons(filepath):
    """Scan file with YARA rules for Cobalt Strike beacons."""
    rules = yara.compile(source=cobalt_strike_rule)
    matches = rules.match(filepath)

    for match in matches:
        print(f"[+] YARA Match: {match.rule}")
        for string_match in match.strings:
            offset = string_match.instances[0].offset
            print(f"    String: {string_match.identifier} at offset 0x{offset:x}")

    return matches

步骤 4：关联网络流量

from dissect.cobaltstrike.c2 import HttpC2Config

def analyze_c2_profile(beacon_config):
    """Analyze malleable C2 profile from beacon configuration."""
    print("\n[+] Malleable C2 Profile Analysis")
    print("=" * 60)

    # HTTP GET configuration
    get_verb = beacon_config.get("SETTING_C2_VERB_GET", "GET")
    get_uri = beacon_config.get("SETTING_C2_REQUEST", "")
    print(f"\n  HTTP GET Request:")
    print(f"    Verb: {get_verb}")
    print(f"    URI: {get_uri}")

    # HTTP POST configuration
    post_verb = beacon_config.get("SETTING_C2_VERB_POST", "POST")
    post_uri = beacon_config.get("SETTING_C2_POSTREQ", "")
    print(f"\n  HTTP POST Request:")
    print(f"    Verb: {post_verb}")
    print(f"    URI: {post_uri}")

    # User Agent
    ua = beacon_config.get("SETTING_USERAGENT", "")
    print(f"\n  User-Agent: {ua}")

    # Host header
    host = beacon_config.get("SETTING_C2_HOSTHEADER", "")
    print(f"  Host Header: {host}")

    # Sleep and jitter for traffic pattern
    sleep_ms = beacon_config.get("SETTING_SLEEPTIME", 60000)
    jitter = beacon_config.get("SETTING_JITTER", 0)
    print(f"\n  Sleep Time: {sleep_ms}ms")
    print(f"  Jitter: {jitter}%")

    # Generate Suricata/Snort signatures
    print(f"\n[+] Suggested Network Signatures:")
    if ua:
        print(f'  alert http any any -> any any (msg:"CS Beacon UA"; '
              f'content:"{ua}"; http_user_agent; sid:1000001; rev:1;)')
    if get_uri:
        print(f'  alert http any any -> any any (msg:"CS Beacon URI"; '
              f'content:"{get_uri}"; http_uri; sid:1000002; rev:1;)')

验证标准

• 成功从 PE 文件或内存转储中提取 Beacon 配置
• 正确识别 C2 服务域名/IP、端口和协议
• 解码可塑性 C2 配置文件参数，显示 HTTP 转换方式
• 提取水印值以便进行归因关联
• 休眠时间和抖动值与观察到的网络 Beacon 间隔相符
• YARA 规则能够检测加壳和未加壳样本中的 Beacon
• 根据提取的 C2 配置文件生成网络特征

参考资料

• SentinelOne CobaltStrikeParser
• dissect.cobaltstrike Library
• SentinelLabs Beacon Configuration Analysis
• Cobalt Strike Staging and Config Extraction
• MITRE ATT&CK - Cobalt Strike S0154