High 7.5Published Oct 14, 2026

CVE-2026-73252Mongoose: Unauthenticated remote heap out-of-bounds read in built-in TLS: off-by-one length check in mg_tls_recv_record() underflows recv_len to SIZE_MAX

Updated under an hour ago (2026-10-19 07:00 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 0.38%, higher than 30% of scored CVEs.

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Exploited in the last 30 days

Mongoose is an embedded web server and network library. Prior to 7.23, the built-in TLS stack selected by MG_TLS_BUILTIN in src/tls_builtin.c accepts a TLS 1.3 record whose decrypted size is exactly the 16-byte authentication tag with no plaintext or ContentType byte. In mg_tls_recv_record(), the msgsz length check permits that record and the recv_len calculation underflows to SIZE_MAX, so a later handshake step treats stale buffer contents as a trusted message with an effectively unbounded length. An unauthenticated malicious TLS peer can trigger a heap out-of-bounds read before certificate or Finished validation, causing a remote denial of service. 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-191, CWE-125
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): 0.38% (percentile 30)
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-hq58-98f5-2wg3x-refsource-confirm
https://github.com/cesanta/mongoose/commit/758e301f0c9a9885c1b716195df5fe6d6ac9d53ex-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.