A stack buffer overflow in the GnuTLS TLS backend of PJSIP (PJProject) occurs when parsing the Subject Alternative Name extension of a peer certificate during the TLS handshake, allowing an attacker with network access to inject a crafted certificate that causes an oversized SAN entry to be written past a fixed‑size stack buffer, which can lead to application termination or, if executable code can be injected, to control‑flow hijack and remote code execution. This flaw is a CWE-121 buffer overrun.

The vulnerability affects PJProject (PJSIP) library versions built with the GnuTLS TLS backend (--with-gnutls) before commit c4a151a; OpenSSL, Apple SecureTransport/Network.framework builds are not affected, and the patch was introduced in commit c4a151a.

The CVSS base score of 8.8 denotes high severity, and no EPSS or KEV listing indicates no public exploitation evidence yet; a network‑positioned attacker can trigger the overflow by presenting a malicious TLS certificate during the handshake before SIP authentication, potentially causing application crash or enabling remote code execution through control‑flow hijack.