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CVE-2026-34873

Trustedfirmware Mbed Tls authentication bypass

9.1 CRITICALEPSS 0.42%
  1. Published1 Apr 2026

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

Trustedfirmware Mbed Tls≥ 3.5.0 < 3.6.6 · ≥ 4.0.0 < 4.1.0

Remediation

Fixed in
Trustedfirmware Mbed Tls≥ 3.6.6

References

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Frequently asked

Is CVE-2026-34873 being actively exploited?

CVE-2026-34873 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.42%.

How severe is CVE-2026-34873?

CVE-2026-34873 has a CVSS 3.1 base score of 9.1, rated critical. EPSS estimates a 0.42% probability of exploitation.

Which products are affected by CVE-2026-34873?

Affected products include Trustedfirmware Mbed Tls.

How do I fix CVE-2026-34873?

Upgrade affected software to a fixed version, for example Trustedfirmware Mbed Tls 3.6.6 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-34873 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.