CVE-2021-4209

A NULL pointer dereference flaw was found in GnuTLS. As Nettle's hash update functions internally call memcpy, providing zero-length input may cause undefined behavior. This flaw leads to a denial of service after authentication in rare circumstances.

This issue is classified as low severity because it requires a very specific and rare set of conditions to be triggered. The vulnerability occurs only when GnuTLS is built with Guile support disabled and when an empty input (zero-length data) is passed during the TLS handshake process.

The crash caused by the NULL pointer dereference is a denial of service, but it does not result in remote code execution or data leakage. Additionally, the affected code path is rarely executed in practice, as it is often replaced by optimized, accelerated implementations. Compilers may also optimize away the issue in most cases, further reducing the likelihood of exploitation.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.