GnuTLS Stack Buffer Overflow in PKCS#11 Init Allows DoS/Code Exec
CVE-2025-9820 Published on January 26, 2026
Gnutls: stack-based buffer overflow in gnutls_pkcs11_token_init() function
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.
Vulnerability Analysis
CVE-2025-9820 is exploitable with local system access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a small impact on availability.
Timeline
Reported to Red Hat.
Made public. 77 days later.
Weakness Type
What is a Stack Overflow Vulnerability?
A 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).
CVE-2025-9820 has been classified to as a Stack Overflow vulnerability or weakness.
Products Associated with CVE-2025-9820
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Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.