Bug 2538911 (CVE-2026-84975)

Summary: CVE-2026-84975 pjproject: PJSIP: Server impersonation via TLS certificate hostname bypass
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: high    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in PJSIP, a multimedia communication library, specifically within its OpenSSL and GnuTLS Transport Layer Security (TLS) backends. This vulnerability allows a remote attacker to bypass server identity verification by using a specially crafted TLS certificate containing an embedded null byte in the Subject Alternative Name (SAN) field. By exploiting this, an attacker can impersonate the target server, intercept communication, and potentially gain access to sensitive information such as user credentials during a Session Initiation Protocol (SIP) session.
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Bug Depends On: 2539361, 2539362, 2539363, 2539364    
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Description OSIDB Bzimport 2026-09-22 21:10:16 UTC 
PJSIP is a free and open source multimedia communication library written in C. In 2.17 and earlier, the OpenSSL and GnuTLS backends in pjlib/src/pj/ssl_sock_ossl.c and pjlib/src/pj/ssl_sock_gtls.c copy DNS SubjectAltName values with string functions that recalculate their length and truncate an embedded NUL byte. With server verification enabled through --tls-verify-server for the PJSIP TLS/SIPS transport, a certificate containing a DNS SubjectAltName formed from the target hostname prefix followed by an embedded NUL and an attacker-controlled suffix can therefore be accepted for the prefix hostname. An attacker who possesses such a certificate from a trusted issuer and can intercept the connection can impersonate the target server, complete the SIP session, and receive REGISTER credentials. The mbedTLS backend is not affected because it preserves the explicit string length. No fixed version is available as of this review.