What’s Vulnerable › Vulnerabilities

CVE-2026-34873

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-01 · updated 2026-06-17
• Weakness: CWE-287

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 products

• TrustedFirmware Mbed TLS: from 3.5.0 before 3.6.6; from 4.0.0 before 4.1.0 — fixed in 3.6.6, 4.1.0

How to fix

Upgrade to a fixed version: TrustedFirmware Mbed TLS 3.6.6, 4.1.0. Check the vendor advisory for mitigations.

References

• https://mbed-tls.readthedocs.io/en/latest/security-advisories/
• https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2026-03-client-impersonation-while-resuming-tls13-session/

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