Vulnerability · Published Oct 14, 2026 · Assigned by GitHub_M
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
High 7.5
In plain English
A high-severity out-of-bounds read in mongoose from cesanta. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 32% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:14 | mongoose | 7.23+ds-1 | DEBIAN-CVE-2026-73252 |
| Ubuntu:26.10 | mongoose | no fix listed | UBUNTU-CVE-2026-73252 |
Affected products (as reported)
Weakness: CWE-191, CWE-125 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
References
- https://github.com/cesanta/mongoose/security/advisories/GHSA-hq58-98f5-2wg3 x_refsource_CONFIRM
- https://github.com/cesanta/mongoose/commit/758e301f0c9a9885c1b716195df5fe6d6ac9d53e x_refsource_MISC
- https://github.com/cesanta/mongoose/releases/tag/7.23 x_refsource_MISC