Is CVE-2026-25832 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-25832 being exploited in the wild.

How severe is CVE-2026-25832?

Low severity, with a CVSS score of 3.7, published 14 September 2026.

Which products and versions are affected?

Mbed TLS Mbed TLS 3.5.0 through 3.6.6, 4.0 through 4.1.1.

Is there a fix for CVE-2026-25832?

A patch was published on 2026-07-07: Patches released in Mbed TLS 3.6.7 and 4.1.2 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-25832 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-25832?

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.

CVE-2026-25832: Mbed TLS TLS 1.3 HelloRetryRequest group validation bypass

CVE-2026-25832 · Severity: low · CVSS 3.7 · Published 2026-09-14

Mbed TLS is a widely-used cryptography library that implements TLS protocol support for secure communications. A vulnerability in its TLS 1.3 client implementation fails to properly validate cryptographic groups selected by a server in HelloRetryRequest messages, allowing a malicious server to bypass the client's group security policy and potentially cause handshake failures.

Quick answers

Is CVE-2026-25832 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-25832 being exploited in the wild.
How severe is CVE-2026-25832?: Low severity, with a CVSS score of 3.7, published 14 September 2026.
Which products and versions are affected?: Mbed TLS Mbed TLS 3.5.0 through 3.6.6, 4.0 through 4.1.1.
Is there a fix for CVE-2026-25832?: A patch was published on 2026-07-07: Patches released in Mbed TLS 3.6.7 and 4.1.2 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-25832 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-25832?: 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 validation bypass in the TLS 1.3 client handshake logic. When processing a HelloRetryRequest, the RFC 8446 specification requires clients to verify that the server-selected group was present in the client's original supported_groups advertisement. Affected Mbed TLS versions (3.5.0–3.6.6 and 4.0–4.1.1) fail to perform this validation correctly. An attacker controlling a TLS server can send a HelloRetryRequest selecting a group outside the client's advertised list, bypassing the client's configured group restrictions. Attack requires network access, a TLS 1.3 client connection, and a configured group policy. Session keys and certificates are not directly compromised, but security or compliance boundaries relying on group restrictions can be violated. Patches are available in Mbed TLS 3.6.7+ and 4.1.2+.

Affected products

Mbed TLS Mbed TLS 3.5.0 through 3.6.6, 4.0 through 4.1.1

Timeline

2026-07-07: disclosed
2026-09-14: advisory
2026-07-07: patched: Patches released in Mbed TLS 3.6.7 and 4.1.2

References

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.