{"id":"CVE-2026-73256","title":"Mongoose is an embedded web server and network library","summary":"Mongoose is an embedded web server and network library. Prior to 7.22, a remote unauthenticated attacker can exploit an HTTP/1.0 reverse-proxy deployment by sending a request with Transfer-Encoding: chunked and conflicting framing. The h…","severity":"critical","cvss":9.1,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N","cwe":["CWE-444"],"vendor":"cesanta","product":"mongoose","affected":["mongoose < 7.22"],"patched":["mongoose 7.22"],"published":"2026-08-20","updated":"2026-09-29","sourceUpdated":"2026-09-29T15:39:13.693","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-73256","references":[{"url":"https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71","label":"security-advisories@github.com"},{"url":"https://github.com/cesanta/mongoose/pull/3611","label":"security-advisories@github.com"},{"url":"https://github.com/cesanta/mongoose/releases/tag/7.22","label":"security-advisories@github.com"},{"url":"https://github.com/cesanta/mongoose/security/advisories/GHSA-mgp5-rjrv-h5j3","label":"security-advisories@github.com"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-73256.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-73256"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-73256"}],"tags":["nvd","csaf","vex","red-hat"],"epss":0.00439,"epssPercentile":0.37963,"ingestedAt":"2026-09-09T21:22:45.545Z","slug":"CVE-2026-73256","body":"## Overview\n\nMongoose is an embedded web server and network library. Prior to 7.22, a remote unauthenticated attacker can exploit an HTTP/1.0 reverse-proxy deployment by sending a request with Transfer-Encoding: chunked and conflicting framing. The http_cb() function in src/http.c tests hm.proto.len with an impossible greater-than-eight condition even though mg_http_parse() requires an eight-byte protocol string, so is_http_1_0 is never set. Mongoose consequently processes chunked encoding that an HTTP/1.0 proxy can ignore, enabling request smuggling and unauthorized access or state changes. This issue is fixed in version 7.22.\n\n## Affected\n\n- `mongoose < 7.22`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `mongoose 7.22`\n\n## Vendor advisories\n\n- **Red Hat VEX** · updated 2026-09-29 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-73256.json)","depth":"midnight","depthScore":50,"depthScoreParts":{"impact":50.1,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}