Vulnerability · Published Apr 2, 2026 · Assigned by mitre
CVE-2026-34877
Critical 9.8
In plain English
A critical-severity unsafe deserialization 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 0.4% (higher than 39% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
An issue was discovered in Mbed TLS versions from 2.19.0 up to 3.6.5, Mbed TLS 4.0.0. Insufficient protection of serialized SSL context or session structures allows an attacker who can modify the serialized structures to induce memory corruption, leading to arbitrary code execution. This is caused by Incorrect Use of Privileged APIs.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | mbedtls | no fix listed | DEBIAN-CVE-2026-34877 |
| Debian:13 | mbedtls | no fix listed | DEBIAN-CVE-2026-34877 |
| Debian:14 | mbedtls | 3.6.6-0.1 | DEBIAN-CVE-2026-34877 |
| Ubuntu:25.10 | mbedtls | no fix listed | UBUNTU-CVE-2026-34877 |
| Ubuntu:26.04:LTS | mbedtls | no fix listed | UBUNTU-CVE-2026-34877 |
| Ubuntu:26.10 | mbedtls | no fix listed | UBUNTU-CVE-2026-34877 |
Affected products (as reported)
Weakness: CWE-250, CWE-502 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H