A heap-buffer-overflow (off-by-one) vulnerability exists in the GnuTLS certtool utility's template parsing logic. When certtool reads certain settings from a template file, it can perform an out-of-bounds NULL pointer write, causing memory corruption and potential denial-of-service. This issue affects GnuTLS packages distributed with Red Hat Enterprise Linux 9 and 10. Red Hat has issued security advisories RHSA-2025:16115 and RHSA-2025:16116 providing patches that fix this vulnerability along with other related GnuTLS issues. The CVSS v3.1 base score is 6.5 (medium severity), indicating network attack vector, low attack complexity, no privileges required, no user interaction, no confidentiality impact, limited integrity impact, and high availability impact.

Successful exploitation of this vulnerability can cause memory corruption resulting in a denial-of-service condition that may crash the affected system. There is no indication of confidentiality loss or privilege escalation from this vulnerability. The impact is limited to integrity and availability, with no known exploitation in the wild.

Red Hat has released official security updates for Red Hat Enterprise Linux 9 and 10 that address this vulnerability. Users should apply the updated gnutls packages as described in Red Hat advisories RHSA-2025:16115 and RHSA-2025:16116. Detailed update instructions are available at https://access.redhat.com/articles/11258. Applying these patches fully mitigates the vulnerability. No additional mitigation steps are required beyond installing the official fixes.