# CVE-2026-34872: mbedtls: An issue was discovered in Mbed TLS 3.5.x and 3.6.x through 3.6.5 and TF-PSA-Crypto 1.0

CVE-2026-34872 is fixed in mbedtls on 1 platform, first by DEBIAN-CVE-2026-34872, released April 1, 2026. It is not reported as exploited. Patch Radar priority: Urgent.

- Web page: https://patchblox.com/security/cve/CVE-2026-34872
- Priority: Urgent
- CVSS: 9.1 (critical)
- EPSS: 0.0021
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Apr 1, 2026

## Description

An issue was discovered in Mbed TLS 3.5.x and 3.6.x through 3.6.5 and TF-PSA-Crypto 1.0. There is a lack of contributory behavior in FFDH due to improper input validation. Using finite-field Diffie-Hellman, the other party can force the shared secret into a small set of values (lack of contributory behavior). This is a problem for protocols that depend on contributory behavior (which is not the case for TLS). The attack can be carried by the peer, or depending on the protocol by an active network attacker (person in the middle).

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | mbedtls Debian 13.5 (trixie) | 3.6.6-0.1~deb13u1 | [DEBIAN-CVE-2026-34872](https://patchblox.com/security/data/fix/linux/debian-cve-2026-34872.md) | Apr 1, 2026 |
| Linux | mbedtls Debian 14 | 3.6.6-0.1 | [DEBIAN-CVE-2026-34872](https://patchblox.com/security/data/fix/linux/debian-cve-2026-34872.md) | Apr 1, 2026 |

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Data as of 2026-11-08T00:53:09Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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