Crawl4AI — Sandbox Escape (CVE-2026-53753)
Date: 2026-06
Affected: kidocode/crawl4ai
Attack vector: sandbox-escape
Category: vulnerability-disclosure
Severity: Critical
CVE: CVE-2026-53753
CWE: CWE-913
CWE-94
CVSS: 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)

Crawl4AI is an open-source LLM friendly web crawler & scraper. Prior to 0.8.7, the _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. The attack requires no authentication (JWT disabled by default) and is triggered via POST /crawl with a crafted extraction schema. This vulnerability is fixed in 0.8.7.


Mitigations:

Architectural layers (MAESTRO):