Critical severity · published Apr 1, 2026
CVE-2026-34873
An issue was discovered in Mbed TLS 3.5.0 through 4.0.0
9.1
CVSS
0.2%
EPSS
No
On KEV
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 vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 15% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MT
Mbed Tls · Trustedfirmware
3.5.0 before 3.6.6; 4.0.0 before 4.1.0 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-34873
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-34873
Vendor Advisory
https://mbed-tls.readthedocs.io/en/latest/security-advisories/
Vendor Advisory
https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2026-03-client-impersonation-while-resuming-tls13-session/
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