CVE-2025-9820: 
GnuTLS vulnerability analysis and mitigation

A low severity vulnerability was discovered in GnuTLS affecting the PKCS#11 token initialization functionality. The vulnerability (CVE-2025-9820) was identified when a token label longer than 32 characters is passed to the gnutlspkcs11token_init function, potentially leading to a stack write buffer overflow. The issue was reported by Luigino Camastra from Aisle Research and was fixed in GnuTLS version 3.8.11 released on November 18, 2025 (GnuTLS Advisory, OSS Security).

The vulnerability occurs in the gnutlspkcs11token_init function where an unbounded memcpy operation is performed into a fixed-size stack buffer of 32 bytes. When a token label exceeding 32 characters is provided, it writes beyond the stack buffer boundaries. The issue stems from the lack of length validation before the memory copy operation. The vulnerability was tracked as issue #1732 in the GnuTLS repository (GitLab Issue).

The vulnerability could lead to stack-based buffer overflow, potentially resulting in process crashes or, depending on system hardening measures, possible code execution. However, the severity is rated as low due to the limited exploitation scope and the requirement for specific PKCS#11 token initialization operations (GnuTLS Advisory).

There are several mitigation options available: 1) Upgrade to GnuTLS version 3.8.11 or later which includes the fix, 2) Applications should validate and reject token labels exceeding the 32-character limit, 3) Compile the library with -DFORTIFYSOURCE=2 which can effectively mitigate the issue (GnuTLS Advisory, OSS Security).