CVE-2026-34873

An issue was discovered in Mbed TLS 3.5.0 through 4.0.0. Client impersonation can occur while...

9.1 CriticalFix available

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.

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None

What an attacker can affect

Confidentiality: High
Integrity: High
Availability: None

Exploit likelihood

0.25%Up 0.2 points since Apr 2, 2026

What each source reports

CVE List Score used 9.1

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.

Record: CVE-2026-34873
CVSS 3.1: 9.1 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Weakness: CWE-287
Updated: 2026-11-02

EUVDEUVD-2026-18064 9.1

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.

Record: EUVD-2026-18064
CVSS 3.1: 9.1 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Updated: 2026-11-02

GitHub AdvisoriesGHSA-q24g-gcpv-7264 9.1

An issue was discovered in Mbed TLS 3.5.0 through 4.0.0. Client impersonation can occur while...

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.

Record: GHSA-q24g-gcpv-7264
CVSS 3.1: 9.1 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Weakness: CWE-287
Updated: 2026-11-02

NVD 9.1

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.

Record: CVE-2026-34873
CVSS 3.1: 9.1 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Weakness: CWE-287
Updated: 2026-11-02

OSV 9.1

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.

Record: CVE-2026-34873
CVSS 3.1: 9.1 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Updated: 2026-11-02

OSVDEBIAN-CVE-2026-34873 9.1

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.

Record: DEBIAN-CVE-2026-34873
CVSS 3.1: 9.1 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Updated: 2026-11-02

OSVUBUNTU-CVE-2026-34873 9.1

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.

Record: UBUNTU-CVE-2026-34873
CVSS 3.1: 9.1 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Updated: 2026-11-02

OSVopenSUSE-SU-2026:10498-1 No score

libeverest-3.6.6-1.1 on GA media

These are all security issues fixed in the libeverest-3.6.6-1.1 package on the GA media of openSUSE Tumbleweed.

Record: openSUSE-SU-2026:10498-1
Updated: 2026-11-02

OSVROOT-OS-DEBIAN-12-CVE-2026-34873 No score

CVE-2026-34873 in mbedtls - Patched by Root

Root has patched CVE-2026-34873 in the mbedtls package for Root:Debian:12. Multiple fixed versions available.

Record: ROOT-OS-DEBIAN-12-CVE-2026-34873
Updated: 2026-11-02

Affected products

trustedfirmware mbed tls

Affected packages

Affected packages
Package	Affected	Fixed
`mbedtls` Debian:12	All versions, plus listed versions 2.28.3-12.28.4-12.28.5-12.28.6-12.28.7-1 Show 18 moreShow less 2.28.7-1.12.28.7-1.1~exp12.28.8-13.6.0-13.6.0-23.6.0-33.6.2-13.6.2-23.6.2-33.6.3-13.6.4-13.6.4-23.6.5-0.13.6.5-0.1~deb13u13.6.6-0.13.6.6-0.1~deb13u13.6.7-23.6.7-3	None known
`mbedtls` Debian:13	before 3.6.6-0.1~deb13u1, plus listed versions 3.6.4-23.6.5-0.13.6.5-0.1~deb13u1	3.6.6-0.1~deb13u1
`mbedtls` Debian:14	before 3.6.6-0.1, plus listed versions 3.6.4-23.6.5-0.13.6.5-0.1~deb13u13.6.6-0.1~deb13u1	3.6.6-0.1
`mbedtls` Root:Debian:12	before 2.28.3-1.root.io.16	2.28.3-1.root.io.162.28.3-1.aikido.17
`rootio-mbedtls` Root:Debian:12	before 2.28.3-1.root.io.16	2.28.3-1.root.io.162.28.3-1.aikido.17
`mbedtls` Ubuntu:16.04:LTS	All versions, plus listed versions 2.1.2-12.2.0-12.2.1-12.2.1-22.2.1-2ubuntu0.12.2.1-2ubuntu0.22.2.1-2ubuntu0.3	None known
`mbedtls` Ubuntu:Pro:18.04:LTS	All versions, plus listed versions 2.5.1-1ubuntu12.6.0-12.7.0-22.8.0-12.8.0-1ubuntu0.1~esm1	None known
`mbedtls` Ubuntu:Pro:20.04:LTS	All versions, plus listed versions 2.16.2-12.16.3-12.16.4-1ubuntu22.16.4-1ubuntu2+esm1	None known
`mbedtls` Ubuntu:Pro:22.04:LTS	All versions, plus listed versions 2.16.9-0.1ubuntu12.16.11-0.1ubuntu12.16.11-0.32.28.0-12.28.0-1build12.28.0-1ubuntu0.1~esm1	None known
`mbedtls` Ubuntu:Pro:24.04:LTS	All versions, plus listed versions 2.28.3-12.28.6-1ubuntu12.28.7-1ubuntu12.28.7-1.1ubuntu12.28.8-12.28.8-1ubuntu0.1~esm1	None known

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Affected packages
Package	Affected	Fixed
`mbedtls` Ubuntu:25.10	All versions, plus listed versions 3.6.2-3ubuntu1	None known
`mbedtls` Ubuntu:26.10	All versions, plus listed versions 3.6.5-0.1ubuntu23.6.6-0.1ubuntu13.6.7-3ubuntu1	None known
`mbedtls` Ubuntu:26.04:LTS	All versions, plus listed versions 3.6.2-3ubuntu13.6.5-0.1ubuntu13.6.5-0.1ubuntu2	None known
`mbedtls` openSUSE:Tumbleweed From an advisory covering 10 CVEs	before 3.6.6-1.1	3.6.6-1.1

History

History
Recorded	Changed	Sources
Nov 6, 2026	affected, facts
Nov 2, 2026	first indexed	CVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-34873 is a critical vulnerability (CVSS 9.1) in Trustedfirmware Mbed Tls, published April 1, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.25%, the 16th percentile. Fixed in mbedtls 3.6.6-0.1~deb13u1.

References

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