CVE-2026-73252

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 3.1

7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

0.4% chance of exploitation in the next 30 days; higher than 31% of CVEs (scores of 2026-10-25)

CWEs

CWE-125, CWE-191

Published

2026-10-14

Modified

2026-10-16

Record from

the NVD, synced 2026-10-19

References

• https://github.com/cesanta/mongoose/commit/758e301f0c9a9885c1b716195df5fe6d6ac9d53e
• https://github.com/cesanta/mongoose/releases/tag/7.23
• https://github.com/cesanta/mongoose/security/advisories/GHSA-hq58-98f5-2wg3
• https://github.com/cesanta/mongoose/security/advisories/GHSA-hq58-98f5-2wg3

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