CVE-2026-53753: Crawl4AI Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-qxjp-w3pj-48m7",
  "modified" : "2026-07-20T21:11:44Z",
  "published" : "2026-06-16T20:13:07Z",
  "aliases" : [ "CVE-2026-53753" ],
  "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",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "crawl4ai"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.8.7"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.8.6"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/unclecode/crawl4ai/security/advisories/GHSA-qxjp-w3pj-48m7"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-53753"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/unclecode/crawl4ai/pull/1855"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/unclecode/crawl4ai/pull/1886"
  }, {
    "type" : "ADVISORY",
    "url" : "https://github.com/advisories/GHSA-qxjp-w3pj-48m7"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/crawl4ai/PYSEC-2026-319.yaml"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/unclecode/crawl4ai"
  }, {
    "type" : "WEB",
    "url" : "https://pypi.org/project/crawl4ai"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-913", "CWE-94" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-16T20:13:07Z",
    "nvd_published_at" : "2026-06-23T19:17:07Z"
  }
}