---
id: CVE-2026-45537
title: OpenSIPS is a Session Initiation Protocol (SIP) server implementation
summary: >-
  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 10…
severity: critical
cvss: 9.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H'
cwe:
  - CWE-120
published: '2026-08-04'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T20:41:31.497'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-45537'
references:
  - url: >-
      https://github.com/OpenSIPS/opensips/commit/4d23613b65579b073784a07a65d3bf52443a4efb
    label: security-advisories@github.com
  - url: >-
      https://github.com/OpenSIPS/opensips/commit/5f103effaf5f372cccffe0b138f16998eba12668
    label: security-advisories@github.com
  - url: >-
      https://github.com/OpenSIPS/opensips/security/advisories/GHSA-v7h4-fwrc-c66v
    label: security-advisories@github.com
  - url: >-
      https://github.com/OpenSIPS/opensips/security/advisories/GHSA-v7h4-fwrc-c66v
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
epss: 0.00626
epssPercentile: 0.47707
ingestedAt: '2026-09-08T21:11:12.267Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.