CVE-2026-45537

Received Received - Intake

Buffer Overflow in OpenSIPS SIP Server

Publication date: 2026-08-04

Last updated on: 2026-08-04

Assigner: GitHub, Inc.

Description

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.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-08-04

Last Modified

2026-08-04

Generated

2026-08-05

AI Q&A

2026-08-05

EPSS Evaluated

N/A

NVD

CVE-2026-45537

Affected Vendors & Products

Vendor	Product	Version / Range
opensips	opensips	to 4.0.0-rc1 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-120	The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer.

Attack-Flow Graph

Executive Summary

This vulnerability is a buffer overflow in OpenSIPS SIP server versions before 3.6.6 and 4.0.0-rc1. The construct_uri() function combines URI components into a fixed 1024-byte buffer without checking length. An attacker can overflow this buffer by providing a long username, corrupting adjacent global data including the disable_503_translation flag, which controls SIP 503 response handling.

Detection Guidance

Detecting this vulnerability requires checking the OpenSIPS version in use. Run 'opensips -v' to verify if the installed version is prior to 3.6.6 or 4.0.0-rc1. If so, the system is vulnerable. Monitor logs for unusual SIP message patterns or routing behavior changes.

Impact Analysis

An attacker could exploit this to alter the server's routing behavior for subsequent messages by setting the disable_503_translation flag. This could lead to improper handling of SIP responses, potentially disrupting VoIP services or enabling further attacks on the SIP infrastructure.

Mitigation Strategies

Upgrade OpenSIPS to version 3.6.6 or 4.0.0-rc1 or later immediately. If upgrading is not possible, restrict network access to OpenSIPS to trusted sources only and monitor for suspicious activity.

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