Vulnerability · Published Apr 1, 2026 · Assigned by mitre
CVE-2026-34872
Critical 9.1
In plain English
A critical-severity security flaw in the mbedtls package (Debian). There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 11% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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).
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | mbedtls | no fix listed | DEBIAN-CVE-2026-34872 |
| Debian:13 | mbedtls | 3.6.6-0.1~deb13u1 | DEBIAN-CVE-2026-34872 |
| Debian:14 | mbedtls | 3.6.6-0.1 | DEBIAN-CVE-2026-34872 |
| Ubuntu:25.10 | mbedtls | no fix listed | UBUNTU-CVE-2026-34872 |
| Ubuntu:26.04:LTS | mbedtls | no fix listed | UBUNTU-CVE-2026-34872 |
| Ubuntu:26.10 | mbedtls | no fix listed | UBUNTU-CVE-2026-34872 |
Affected products (as reported)
Weakness: CWE-347 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N