Out-of-bounds Read in Cesanta Mongoose
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.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
- Cesanta Mongoose — versions < 7.23
Weakness classification (CWE)
References
Frequently asked questions
- What is CVE-2026-73252?
- CVE-2026-73252 is a high-severity vulnerability in Cesanta Mongoose, classified under Out-of-bounds Read. CVSS score: 7.5/10. Published 2026-10-14.
- How severe is CVE-2026-73252?
- High severity. CVSS v3 base score is 7.5 out of 10.