Vulnerability · Published Apr 1, 2026 · Assigned by mitre
CVE-2026-34873
Critical 9.1
In plain English
A critical-severity improper authentication 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 0.3% (higher than 17% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)9.1Critical
Exploit odds (30 days)0.3%top 83.5% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
An issue was discovered in Mbed TLS 3.5.0 through 4.0.0. Client impersonation can occur while resuming a TLS 1.3 session.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | mbedtls | no fix listed | DEBIAN-CVE-2026-34873 |
| Debian:13 | mbedtls | 3.6.6-0.1~deb13u1 | DEBIAN-CVE-2026-34873 |
| Debian:14 | mbedtls | 3.6.6-0.1 | DEBIAN-CVE-2026-34873 |
| Ubuntu:25.10 | mbedtls | no fix listed | UBUNTU-CVE-2026-34873 |
| Ubuntu:26.04:LTS | mbedtls | no fix listed | UBUNTU-CVE-2026-34873 |
| Ubuntu:26.10 | mbedtls | no fix listed | UBUNTU-CVE-2026-34873 |
Affected products (as reported)
Weakness: CWE-287 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N