CVE-2026-34873
Client Impersonation in Mbed TLS 3.5.0–4.0.0 TLS 1.3 Resume
Publication date: 2026-04-01
Last updated on: 2026-04-07
Assigner: MITRE
Description
Description
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| arm | mbed_tls | From 3.5.0 (inc) to 3.6.6 (exc) |
| arm | mbed_tls | From 4.0.0 (inc) to 4.1.0 (exc) |
Helpful Resources
Exploitability
| 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
AI Powered Q&A
Can you explain this vulnerability to me?
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.
How can this vulnerability impact me? :
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.
How does this vulnerability affect compliance with common standards and regulations (like GDPR, HIPAA)?:
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.
What immediate steps should I take to mitigate this vulnerability?
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.