CVE-2026-34877
Published: 02 April 2026
Summary
CVE-2026-34877 is a critical-severity Execution with Unnecessary Privileges (CWE-250) vulnerability in Arm Mbed Tls. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 44.6th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 RA-5 (Vulnerability Monitoring and Scanning) and SI-16 (Memory Protection).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Directly mandates identification, reporting, and correction of flaws like the serialization vulnerability in Mbed TLS through timely patching.
Implements memory protection mechanisms such as DEP and ASLR to prevent arbitrary code execution resulting from memory corruption induced by modified serialized SSL structures.
Enables ongoing vulnerability scanning to identify systems using vulnerable Mbed TLS versions affected by CVE-2026-34877.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
CVE-2026-34877 enables remote unauthenticated exploitation of public-facing applications using vulnerable Mbed TLS library via memory corruption in serialized SSL structures, leading to arbitrary code execution.
NVD Description
An issue was discovered in Mbed TLS versions from 2.19.0 up to 3.6.5, Mbed TLS 4.0.0. Insufficient protection of serialized SSL context or session structures allows an attacker who can modify the serialized structures to induce memory corruption, leading to…
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arbitrary code execution. This is caused by Incorrect Use of Privileged APIs.
Deeper analysisAI
CVE-2026-34877 is a critical vulnerability affecting Mbed TLS cryptographic library versions from 2.19.0 up to 3.6.5, as well as version 4.0.0. The flaw stems from insufficient protection of serialized SSL context or session structures due to incorrect use of privileged APIs (CWE-250, CWE-502). This allows an attacker with the ability to modify these serialized structures to induce memory corruption, potentially leading to arbitrary code execution.
The vulnerability carries a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), making it exploitable remotely over the network by unauthenticated attackers with low complexity and no user interaction required. Successful exploitation enables full compromise of the affected system through memory corruption and arbitrary code execution, granting high-impact access to confidentiality, integrity, and availability.
Mitigation guidance is detailed in the official Mbed TLS security advisories at https://mbed-tls.readthedocs.io/en/latest/security-advisories/ and the specific advisory at https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2026-03-serialized-data/, published around April 2026. Security practitioners should review these for patch availability, upgrade recommendations, and any interim workarounds to protect deployments using vulnerable Mbed TLS versions.
Details
- CWE(s)