CVE-2026-45537 — OpenSIPS is a Session Initiation Protocol (SIP) server implementation.¶
Key facts
CVE-2026-45537 is a Critical (9.1) vulnerability: OpenSIPS is a Session Initiation Protocol (SIP) server implementation.. This entry ships a detection-only PoC and a Docker test lab.
| CVE | CVE-2026-45537 |
| Severity | Critical (9.1) |
| Detection / prevention | — |
| PoC | poc.py |
| Source | 2026/CVE-2026-45537/ |
Details¶
English | 한국어
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.
Vulnerability Details¶
| Property | Value |
|---|---|
| CVE ID | CVE-2026-45537 |
| CVSS Score | 9.1 |
Proof of Concept¶
Download¶
# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2026/CVE-2026-45537/poc.py
Usage¶
# Run PoC against target
python3 poc.py --target <TARGET_URL>
# With authentication
python3 poc.py --target <TARGET_URL> --username <USER> --password <PASS>
⚠️ Warning: This PoC is for authorized security testing only. It uses detection-only techniques and does not exploit or damage target systems.
Test Lab¶
This repository includes a Docker-based test environment with both vulnerable and patched applications.
Quick Start¶
# Clone and navigate to CVE directory
cd CVE-2026-45537
# Start both applications
docker-compose up -d
# Run tests
./run-tests.sh # Linux/Mac
./run-tests.ps1 # Windows PowerShell
Application Endpoints¶
| Application | URL | Status |
|---|---|---|
| Vulnerable App | http://localhost:8080 | Shows vulnerability |
| Patched App | http://localhost:8081 | Demonstrates fix |
Directory Structure¶
├── README.md # English documentation
├── README_KO.md # Korean documentation
├── poc.py # PoC detection script
├── docker-compose.yml # Container orchestration
├── run-tests.sh # Linux/Mac test runner
├── run-tests.ps1 # Windows test runner
├── vulnerable-app/ # Vulnerable version
│ ├── app.py
│ ├── Dockerfile
│ └── requirements.txt
└── patched-app/ # Fixed version
├── app.py
├── Dockerfile
└── requirements.txt
References¶
- https://github.com/OpenSIPS/opensips/commit/4d23613b65579b073784a07a65d3bf52443a4efb
- https://github.com/OpenSIPS/opensips/commit/5f103effaf5f372cccffe0b138f16998eba12668
- https://github.com/OpenSIPS/opensips/security/advisories/GHSA-v7h4-fwrc-c66v
- https://github.com/OpenSIPS/opensips/security/advisories/GHSA-v7h4-fwrc-c66v
Generated by PoC Generator on 2026-08-10T07:57:42.915670809
Frequently asked questions¶
What is CVE-2026-45537?¶
CVE-2026-45537 is a Critical (9.1) vulnerability: OpenSIPS is a Session Initiation Protocol (SIP) server implementation.. This entry ships a detection-only PoC and a Docker test lab.
How do I detect CVE-2026-45537?¶
Run the detection-only PoC included with this entry against your Docker test lab to confirm whether a target is affected; pair it with your own IDS logging.
How do I block or mitigate CVE-2026-45537?¶
Upgrade to a fixed version per the vendor advisory; the NVD record lists the affected versions. Use the included PoC to verify your remediation.
For authorized security testing and research only. See the full source and NVD record.