CVE-2026-45538: OpenSIPS stack buffer overflow in sip_to_json header parsing

CVE-2026-45538 · Severity: critical · CVSS 9.8 · Published 2026-08-04

OpenSIPS is a Session Initiation Protocol (SIP) server that routes and processes phone calls and messaging traffic. A vulnerability in the sip_to_json() function allows an attacker to crash the SIP server or execute arbitrary code by sending a specially crafted SIP message with an exceptionally long header name. Since this function processes unauthenticated incoming messages, a single malicious packet sent to the default SIP port can disable the service or compromise the entire system.

Technologies: OpenSIPS. Vendors: OpenSIPS.

Quick answers

Is CVE-2026-45538 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-45538 being exploited in the wild.
How severe is CVE-2026-45538?
Critical severity, with a CVSS score of 9.8, published 4 August 2026.
Which products and versions are affected?
OpenSIPS 3.6.0 through 3.6.5, 4.0.0 and prior.
Is there a fix for CVE-2026-45538?
A patch was published on 2026: Fixed in versions 3.6.6 and 4.0.1 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-45538 attacked?
It is attacked over the network, in a hosted service.
Am I affected by CVE-2026-45538?
Check whether you run OpenSIPS at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability is a stack buffer overflow in the sip_to_json() function within modules/sipmsgops/sipmsgops.c (lines 2118–2152). The function copies SIP header names into a fixed 255-byte stack buffer using memcpy() without bounds checking, despite the SIP parser allowing header names up to approximately 65,000 bytes. An attacker sends a SIP message (INVITE, REGISTER, etc.) with a custom header whose name exceeds 255 bytes, triggering the overflow. The overflow is fully attacker-controlled in both size and content, allowing corruption of saved registers and the return address on the stack. No authentication is required; the function processes messages before any SIP auth checks. Exploitation results in immediate denial of service (crash) on hardened builds, or remote code execution via return-address hijacking on standard builds without stack protections. Patches were released in versions 3.6.6 and 4.0.1.

Affected products

  • OpenSIPS OpenSIPS 3.6.0 through 3.6.5, 4.0.0 and prior

Timeline

  • 2026-05-21: disclosed: GitHub Security Advisory GHSA-37wc-5j8j-95x3 published
  • 2026: patched: Fixed in versions 3.6.6 and 4.0.1
  • 2026-08-04: advisory: NVD CVE-2026-45538 published

References

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