{"id":"CVE-2026-73261","summary":"Mongoose: handle_opt() missing opts[1] \u003e len check — 1-byte OOB read corrupts TCP MSS, silences mg_send() per connection","details":"Mongoose is an embedded web server and network library. Prior to 7.23, the built-in TCP/IP stack enabled by MG_ENABLE_TCPIP in src/net_builtin.c does not reject a TCP option whose declared opts[1] length exceeds the remaining option bytes. In handle_opt(), a NOP followed by a truncated MSS option causes opts[3] to be read outside the declared options area and used as the low byte of dmss. An unauthenticated remote peer can corrupt the per-connection MSS value so later mg_send() calls transmit truncated or zero-length application payloads while the TCP connection otherwise appears healthy. This issue is fixed in version 7.23.","aliases":["GHSA-3fmr-92g4-wchx"],"modified":"2026-10-15T10:47:31.561983470Z","published":"2026-10-14T18:25:41.102Z","database_specific":{"cna_assigner":"GitHub_M","cwe_ids":["CWE-125","CWE-20"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/73xxx/CVE-2026-73261.json"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/73xxx/CVE-2026-73261.json"},{"type":"FIX","url":"https://github.com/cesanta/mongoose/commit/cc7c6d2d18c28fcc6d085633dddd88402946140a"},{"type":"WEB","url":"https://github.com/cesanta/mongoose/releases/tag/7.23"},{"type":"ADVISORY","url":"https://github.com/cesanta/mongoose/security/advisories/GHSA-3fmr-92g4-wchx"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-73261"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/cesanta/mongoose","events":[{"introduced":"0"},{"fixed":"02bdbb9ed6f0a8f7c42228c6e7cb35d748b60551"}],"database_specific":{"extracted_events":[{"introduced":"0"},{"fixed":"7.23"}],"source":"AFFECTED_FIELD"}}],"versions":["7.22","7.21","7.20","7.19","7.18","7.17","7.16","7.15","7.14","7.13","7.12","7.11","7.8","7.7","7.6","7.5","7.4","7.3","7.2","7.1","7.0","6.18","6.17","6.16","6.15","6.14","6.13","6.12","6.11","6.10","6.9","6.7","6.6","6.5","6.4","6.3","6.2","6.1","6.0","5.6","5.5_20140120","5.5","5.4","5.3","5.2","5.1","5.0","4.1","4.0","3.8","3.7","3.6","3.5","3.4","3.3","3.2"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-73261.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"}]}