CVE-2026-45537
CriticalCVSS 9.1Summary
OpenSIPS prior to versions 3.6.6 and 4.0.0-rc1 contains a buffer overflow in the construct_uri() function, which concatenates URI components into a fixed 1024-byte buffer without bounds checking. An attacker can control the username to overflow the buffer and overwrite adjacent global data, including the disable_503_translation flag, altering routing behavior.
Risk Assessment
Risk of SIP server integrity compromise, routing logic alteration, and potential disruption of VoIP services.
Recommendation
Upgrade OpenSIPS to version 3.6.6 or 4.0.0-rc1. If not possible, restrict access to the server and monitor for unusual SIP requests.
Original NVD description (English source)
OpenSIPS is a Session Initiation Protocol (SIP) server implementation. In versions prior to 3.6.6 and 4.0.0-rc1, the construct_uri() function concatenates multiple URI components (protocol, username, domain, port, params) into a fixed 1024-byte global BSS buffer without any bounds checking. When a routing script calls construct_uri() with an attacker-controlled username, a combined component length exceeding 1024 bytes overflows the buffer, corrupting adjacent global data with attacker-controlled content. The overflow reaches disable_503_translation, a global flag controlling SIP 503 response handling, allowing an attacker to deterministically set the flag via the URI username and alter the server's routing behavior for subsequent messages. Because the same buffer is shared with contact_builder(), the overflow also corrupts that function's data, and without a memory sanitizer the adjacent globals are silently overwritten on every request containing a long username. This issue has been fixed in versions 3.6.6 and 4.0.0-rc1.