CVE-2026-34873

Analyzed Analyzed - Analysis Complete

Client Impersonation in Mbed TLS 3.5.0–4.0.0 TLS 1.3 Resume

Publication date: 2026-04-01

Last updated on: 2026-06-05

Assigner: MITRE

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 Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-04-01

Last Modified

2026-06-05

Generated

2026-07-06

AI Q&A

2026-04-02

EPSS Evaluated

2026-07-05

NVD

CVE-2026-34873

Affected Vendors & Products

Vendor	Product	Version / Range
trustedfirmware	mbed_tls	From 4.0.0 (inc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-287	When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.

Attack-Flow Graph

Impact Analysis

An attacker could impersonate a client when resuming a TLS 1.3 session, potentially allowing unauthorized access or interception of communications that are expected to be secure.

Compliance Impact

The provided information does not specify how the client impersonation vulnerability in Mbed TLS affects compliance with common standards and regulations such as GDPR or HIPAA.

Mitigation Strategies

To mitigate the client impersonation vulnerability in Mbed TLS during TLS 1.3 session resumption, you should update Mbed TLS to a fixed version where this issue is resolved.

The advisory mentions available work-arounds and fix commits, so applying the latest security patches or upgrading to a version beyond 4.0.0 that addresses this vulnerability is recommended.

Executive Summary

This vulnerability exists in Mbed TLS versions 3.5.0 through 4.0.0 and involves client impersonation during the resumption of a TLS 1.3 session.

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