High 7.5Published Oct 14, 2026

CVE-2026-73261Mongoose: handle_opt() missing opts[1] > len check — 1-byte OOB read corrupts TCP MSS, silences mg_send() per connection

Updated under an hour ago (2026-10-19 06:10 UTC)

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It affects cesanta mongoose. Add what you run to find out whether that includes you.

EPSS puts the chance of exploitation in the next 30 days at 0.35%, higher than 27% of scored CVEs.

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Every CVE for cesanta mongoose

Exploited in the last 30 days

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.

CVSS: 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE): CWE-20, CWE-125
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): 0.35% (percentile 27)
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: Oct 14, 2026
First seen by InfoSec Signals: Oct 14, 2026

Affected products

Affected products

cesanta mongoose cesanta:mongoose (from the name)	before 7.23	CNA record

References

https://github.com/cesanta/mongoose/security/advisories/GHSA-3fmr-92g4-wchxx-refsource-confirm
https://github.com/cesanta/mongoose/commit/cc7c6d2d18c28fcc6d085633dddd88402946140ax-refsource-misc
https://github.com/cesanta/mongoose/releases/tag/7.23x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.