mbed TLS up to 3.5.0/4.0.0 TLS 1.3 Session improper authentication

CVSS Meta Temp Score
CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.
Current Exploit Price (≈)
Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.
CTI Interest Score
Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
7.7$0-$5k0.00

Summaryinfo

A vulnerability was found in mbed TLS up to 3.5.0/4.0.0. It has been classified as critical. This affects an unknown part of the component TLS 1.3 Session Handler. Performing a manipulation results in Remote Privilege Escalation. This vulnerability is reported as CVE-2026-34873. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability classified as critical has been found in mbed TLS up to 3.5.0/4.0.0. This affects an unknown code block of the component TLS 1.3 Session Handler. The manipulation with an unknown input leads to a remote privilege escalation vulnerability. CWE is classifying the issue as CWE-287. When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at mbed-tls.readthedocs.io. This vulnerability is uniquely identified as CVE-2026-34873 since 03/31/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 06/06/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Name

Version

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 7.7
VulDB Meta Temp Score: 7.7

VulDB Base Score: 6.3
VulDB Temp Score: 6.3
VulDB Vector: 🔒
VulDB Reliability: 🔍

ADP CISA Base Score: 9.1
ADP CISA Vector: 🔒

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Improper authentication
CWE: CWE-287
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: no mitigation known
Status: 🔍

0-Day Time: 🔒

Timelineinfo

03/31/2026 CVE reserved
04/02/2026 +2 days Advisory disclosed
04/02/2026 +0 days VulDB entry created
06/06/2026 +65 days VulDB entry last update

Sourcesinfo

Advisory: mbed-tls.readthedocs.io
Status: Not defined

CVE: CVE-2026-34873 (🔒)
GCVE (CVE): GCVE-0-2026-34873
GCVE (VulDB): GCVE-100-354807

Entryinfo

Created: 04/02/2026 02:44
Updated: 06/06/2026 20:04
Changes: 04/02/2026 02:44 (50), 06/06/2026 20:04 (13)
Complete: 🔍
Cache ID: 216::103

Be aware that VulDB is the high quality source for vulnerability data.

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