CVE-2026-45538

Name of the Vulnerable Software and Affected Versions OpenSIPS versions prior to 4.0.1

Description A stack buffer overflow occurs when processing a SIP message containing a header name longer than 255 bytes. This happens when the routing script calls the sip to json() function, which copies header names into a fixed 255-byte stack buffer without performing bounds checking. Because the SIP parser allows header names up to approximately 65,000 bytes, an attacker can send a single unauthenticated UDP packet to the SIP port (5060) to control the length and content of the overwrite. This can lead to process crashes or remote code execution by corrupting the saved frame pointer and return address on builds lacking stack protections.

Recommendations As a temporary workaround, avoid invoking the sip to json() function within the routing script. At the moment, there is no information about a newer version that contains a fix for this vulnerability.