CVE-2026-34873
Mbed TLS TLS 1.3 session resumption client impersonation.
Is CVE-2026-34873 being exploited?
Not confirmed. CVE-2026-34873 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.24% probability of exploitation in the next 30 days.
How severe is CVE-2026-34873?
CVE-2026-34873 is rated Critical with a CVSS score of 9.1. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-34873?
Yes. A fix has been recorded for CVE-2026-34873. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-34873 affect?
CVE-2026-34873 affects Mbed TLS 3.5.0-4.0.0. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-34873?
Upgrade to fixed Mbed TLS release when available.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Impersonates TLS client during session resumption, enabling MITM or data exposure.
Immediate action required