Quick answers
- Is CVE-2026-11404 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-11404 being exploited in the wild.
- How severe is CVE-2026-11404?
- High severity, with a CVSS score of 7.5, published 9 July 2026.
- Which products and versions are affected?
- Cesanta Mongoose before 7.22.
- Is there a fix for CVE-2026-11404?
- A patch was published on 2026-06-24: Version 7.22 released with fix Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-11404 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-11404?
- Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
An out-of-bounds read vulnerability exists in the mg_tls_server_recv_hello() function within Cesanta Mongoose's built-in TLS implementation (MG_TLS_BUILTIN). The root cause is the use of an attacker-controlled session_id_len byte from a TLS ClientHello message as a buffer index without proper validation against the actual length of the received data. A remote, unauthenticated attacker can exploit this by sending a single crafted ClientHello packet with an oversized session ID length. This causes the server to read past the receive buffer, resulting in a crash and denial-of-service for any service utilizing the built-in TLS stack (such as HTTPS, MQTTS, or WSS). The issue is resolved in version 7.22.
Affected products
- Cesanta Mongoose before 7.22
Timeline
- 2026-06-24: patched: Version 7.22 released with fix
- 2026-07-09: disclosed: CVE published and advisory released