id: PYSEC-2026-319
published: "2026-06-29T11:50:52.380343Z"
modified: "2026-07-01T20:22:50.664862Z"
aliases:
- CVE-2026-53753
- GHSA-qxjp-w3pj-48m7
summary: "Crawl4AI: AST Sandbox Escape via gi_frame.f_back Chain - Pre-Auth RCE in Docker API"
details: "### Summary\n\nThe `_safe_eval_expression()` function in the computed fields feature uses an AST validator that only blocks attributes starting with underscore. Python generator and frame object attributes (`gi_frame`, `f_back`, `f_builtins`) do NOT start with underscore, enabling a complete sandbox escape to achieve arbitrary code execution.\n\nThe attack requires no authentication (JWT disabled by default) and is triggered via `POST /crawl` with a crafted extraction schema.\n\n### Attack Vector\n\nAn attacker sends a `POST /crawl` request with a `JsonCssExtractionStrategy` schema containing a malicious computed field expression that:\n1. Creates a generator to access `gi_frame`\n2. Walks the frame chain via `f_back`\n3. Reaches `f_builtins` containing the real `__import__`\n4. Imports `os` and executes arbitrary commands\n \n### Impact\n\nUnauthenticated remote code execution inside the Docker container. An attacker can execute arbitrary system commands, read/write files, and exfiltrate secrets.\n\n### Fix Details\n\n1. Removed `eval()` from computed field expression path entirely -- expressions now log a warning and return default value\n2. Deleted `_safe_eval_expression()` function and `_SAFE_EVAL_BUILTINS` (dead security-sensitive code)\n3. `function` key with Python callables still works for SDK users\n4. Replaced `eval()` in `/config/dump` with JSON-based input validated by Pydantic\n5. Fixed hook_manager sandbox: stripped `__builtins__`, `__loader__`, `__spec__` from injected modules; removed `getattr`, `setattr`, `type`, `__build_class__` from allowed builtins\n \n### Workarounds\n\n1. Upgrade to the patched version (recommended)\n2. Enable JWT authentication via `CRAWL4AI_API_TOKEN` environment variable\n3. Restrict network access to the Docker API\n\n### Credits\n\n- Song Binglin ([q1uf3ng](https://github.com/q1uf3ng)) - reported the AST sandbox escape\n- by111 ([August829](https://github.com/August829)) - reported the hook sandbox `__builtins__` escape and hardcoded JWT secret bypass\n - [jannahopp](https://github.com/jannahopp) - PR #1855 proposing eval removal\n - [ntohidi](https://github.com/ntohidi) - PR #1886 proposing allowlist approach"
affected:
- package:
    name: crawl4ai
    ecosystem: PyPI
    purl: pkg:pypi/crawl4ai
  ranges:
  - type: ECOSYSTEM
    events:
    - introduced: "0"
    - fixed: 0.8.7
  versions:
  - 0.3.0
  - 0.3.1
  - 0.3.2
  - 0.3.3
  - 0.3.4
  - 0.3.5
  - 0.3.6
  - 0.3.7
  - 0.3.71
  - 0.3.72
  - 0.3.73
  - 0.3.731
  - 0.3.74
  - 0.3.741
  - 0.3.742
  - 0.3.743
  - 0.3.744
  - 0.3.745
  - 0.3.746
  - 0.3.8
  - 0.4.0
  - 0.4.1
  - 0.4.21
  - 0.4.22
  - 0.4.23
  - 0.4.24
  - 0.4.241
  - 0.4.242
  - 0.4.243
  - 0.4.244
  - 0.4.245
  - 0.4.246
  - 0.4.247
  - 0.4.248
  - 0.4.248b3
  - 0.4.3b1
  - 0.4.3b2
  - 0.4.3b3
  - 0.5.0
  - 0.5.0.post1
  - 0.5.0.post2
  - 0.5.0.post3
  - 0.5.0.post4
  - 0.5.0.post5
  - 0.5.0.post6
  - 0.5.0.post7
  - 0.5.0.post8
  - 0.6.0
  - 0.6.0rc1
  - 0.6.1
  - 0.6.2
  - 0.6.3
  - 0.7.0
  - 0.7.1
  - 0.7.2
  - 0.7.3
  - 0.7.4
  - 0.7.5
  - 0.7.6
  - 0.7.7
  - 0.7.8
  - 0.8.0
  - 0.8.5
  - 0.8.6
references:
- type: WEB
  url: https://github.com/unclecode/crawl4ai/security/advisories/GHSA-qxjp-w3pj-48m7
- type: WEB
  url: https://github.com/unclecode/crawl4ai/pull/1855
- type: WEB
  url: https://github.com/unclecode/crawl4ai/pull/1886
- type: PACKAGE
  url: https://github.com/unclecode/crawl4ai
- type: PACKAGE
  url: https://pypi.org/project/crawl4ai
- type: ADVISORY
  url: https://github.com/advisories/GHSA-qxjp-w3pj-48m7
- type: ADVISORY
  url: https://nvd.nist.gov/vuln/detail/CVE-2026-53753
severity:
- type: CVSS_V3
  score: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H