{"id":"CVE-2026-66731","summary":"facil.io 0.7.5 - 0.7.6 HTTP/1.1 Chunked Transfer Encoding Parser Crash DoS","details":"facil.io 0.7.5 through 0.7.6 contains a denial-of-service vulnerability in the HTTP/1.1 chunked transfer encoding parser that allows unauthenticated remote attackers to crash the server by sending a negative chunk size value. Attackers can send a single POST request with a Transfer-Encoding: chunked header containing a leading minus sign in the chunk size field, causing the parser in http1_parser.h to compute a large positive integer from the negated value, corrupting internal state and moving the read pointer into unmapped memory resulting in a fault.","modified":"2026-08-12T03:51:47.914507106Z","published":"2026-07-27T16:57:01.077Z","database_specific":{"cna_assigner":"VulnCheck","cwe_ids":["CWE-125"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/66xxx/CVE-2026-66731.json"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/66xxx/CVE-2026-66731.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-66731"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/facil-io-http-chunked-transfer-encoding-parser-crash-dos"},{"type":"PACKAGE","url":"https://github.com/boazsegev/facil.io"},{"type":"EVIDENCE","url":"https://github.com/theopaid/Negative-Chunk-Size-Parsing-Causes-Memory-Corruption-in-facil.io-leading-to-Server-Crash"},{"type":"EVIDENCE","url":"https://tpaidakis.com/writeups/facilio-parser-dos/"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/boazsegev/facil.io","events":[{"introduced":"063c9bb86e14bae7441d2e37ab7207d9839a98ce"},{"last_affected":"512a354dbd31e1895647df852d1565f9d408ed91"}],"database_specific":{"extracted_events":[{"introduced":"0.7.5"},{"last_affected":"0.7.6"}],"source":"AFFECTED_FIELD"}}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-66731.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"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"}]}