# CVE-2026-73251: Mongoose TLS certificate-chain verification bypass with CA bundles

Source: https://junglewise.ai/threats/cve-2026-73251-mongoose-tls-certificate-chain-verification-bypass-with-ca  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-20. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-73251 · Severity: info · Published 2026-08-20

Mongoose is an embedded web server and network library used in IoT and embedded systems. Prior to version 7.23, an attacker on the network can impersonate a legitimate TLS server by forging a self-signed certificate when Mongoose is configured with a multi-certificate CA bundle. This allows attackers to intercept encrypted connections, steal credentials, modify traffic, and inject malicious responses without detection.

## Quick answers

**Is CVE-2026-73251 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-73251 being exploited in the wild.

**How severe is CVE-2026-73251?** Informational severity, published 20 August 2026.

**Which products and versions are affected?** Cesanta Mongoose prior to 7.23.

**Is there a fix for CVE-2026-73251?** A patch was published on 2026-08-12: Fixed in version 7.23 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-73251 attacked?** It is attacked over the network or from the adjacent network, in a software library.

**Am I affected by CVE-2026-73251?** 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

The vulnerability is a TLS certificate verification bypass in the built-in TLS implementation. When mg_tls_init() loads a multi-certificate CA bundle, it stores the bundle in tls->ca_bundle_der but leaves tls->ca_der.len at zero. The mg_tls_recv_cert() function then uses tls_bundle_find() to match certificates by Common Name without calling mg_tls_verify_cert_signature(), allowing a forged self-signed certificate to pass hostname verification and CertificateVerify checks. The attack requires network position to intercept TLS connections but no authentication or user interaction. An attacker can perform man-in-the-middle attacks to intercept, eavesdrop on, and modify encrypted communications. The vulnerability is fixed in Mongoose 7.23.

## Affected products

- Cesanta Mongoose prior to 7.23

## Timeline

- 2026-08-20: disclosed
- 2026-08-12: patched: Fixed in version 7.23

## References

- [https://github.com/cesanta/mongoose/commit/2988bc9df3a5efc9539471cb7455975fa25df483](https://github.com/cesanta/mongoose/commit/2988bc9df3a5efc9539471cb7455975fa25df483)
- [https://github.com/cesanta/mongoose/releases/tag/7.23](https://github.com/cesanta/mongoose/releases/tag/7.23)