CVE-2026-34873

CRITICALNVD 9.19.1—

9.1

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.

CVSS v3: 9.1
EG Score: 9.1(medium)
EPSS: 12.2%
KEV: Not listed

Published

April 1, 2026

Last Modified

April 7, 2026

Advisory Details (2)

Auto-updated May 20, 2026

No patch confirmed yet.

generic

Client impersonation while resuming a TLS 1.3 session (CVE-2026-34873) — Mbed TLS documentation

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

generic

Security Advisories — Mbed TLS documentation

https://mbed-tls.readthedocs.io/en/latest/security-advisories/

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

CWE-287Improper Authentication

Data Freshness Timeline

(refreshed 16× in last 7d / 20× in last 30d)

Every time one of our enrichment pipelines (NVD, MITRE cvelistV5, EPSS, CISA KEV, GHSA, OSV, vendor advisories) ran against this CVE. Most recent first.

2026-05-31 22:30 UTCepss_batch
2026-05-31 22:30 UTCepss_batch
2026-05-31 00:16 UTCepss_batch
2026-05-31 00:16 UTCepss_batch
2026-05-31 00:16 UTCepss_batch
2026-05-29 13:44 UTCepss_batch
2026-05-29 13:44 UTCepss_batch
2026-05-28 13:44 UTCepss_batch
2026-05-28 13:44 UTCepss_batch
2026-05-28 13:44 UTCepss_batch
2026-05-27 13:40 UTCepss_batch
2026-05-27 13:40 UTCepss_batch
2026-05-27 13:40 UTCepss_batch
2026-05-26 13:44 UTCepss_batch
2026-05-26 07:18 UTCepss_batch
2026-05-26 07:18 UTCepss_batch
2026-05-20 22:38 UTCepss_batch
2026-05-20 22:38 UTCepss_batch
2026-05-20 19:33 UTCEG score recompute
2026-05-20 19:33 UTCGHSA enrichment

Frequently asked(5)

What is CVE-2026-34873?

CVE-2026-34873 is a critical vulnerability published on April 1, 2026. 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.

When was CVE-2026-34873 disclosed?

CVE-2026-34873 was first published in the National Vulnerability Database on April 1, 2026, with the most recent update on April 7, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2026-34873 actively exploited?

CVE-2026-34873 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 12.2% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

What is the CVSS score of CVE-2026-34873?

CVE-2026-34873 has a CVSS v3 base score of 9.1 (NVD).

How do I remediate CVE-2026-34873?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-34873, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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CVE-2026-34873

📅 Published

🔄 Last Modified

📋 Advisory Details (2)