CVE-2025-9820: gnutls Stack-based Buffer Overflow

Vulnerability summary

CVE-2025-9820 is a medium (CVSS 4.0) Stack-based Buffer Overflow vulnerability in gnutls. EPSS estimates a 0.23% chance of exploitation in the next 30 days, higher than 12.4% of scored vulnerabilities.

Timeline

1. 26-01-2026
   PublishedVulnerability first disclosed.
2. 14-10-2026
   Last modifiedVulnerability information updated.

Description

A flaw was found in the GnuTLS library, specifically in the gnutls_pkcs11_token_init() function that handles PKCS#11 token initialization. When a token label longer than expected is processed, the function writes past the end of a fixed-size stack buffer. This programming error can cause the application using GnuTLS to crash or, in certain conditions, be exploited for code execution. As a result, systems or applications relying on GnuTLS may be vulnerable to a denial of service or local privilege escalation attacks.

• CWE-121Stack-based Buffer OverflowA stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).