CVE-2025-11677 Use After Free in libwebsockets WebSocket server
A use-after-free flaw in libwebsockets can cause denial of service in specific configurations involving custom HTTP upgrade callbacks.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-11677?
CVE-2025-11677 is a medium-severity use after free vulnerability in warmcat libwebsockets, published on 20 Oct 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Use After Free in WebSocket server implementation in lws_handshake_server in warmcat libwebsockets may allow an attacker, in specific configurations where the user provides a callback function that handles LWS_CALLBACK_HTTP_CONFIRM_UPGRADE, to achieve denial of service.
Weakness: CWE-416
Which versions are affected by CVE-2025-11677?
How do I fix CVE-2025-11677?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2025-11677 being exploited?
There is no known exploitation of CVE-2025-11677 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-11677, DEBIAN-CVE-2025-11677, GHSA-fpc8-25p9-jfmr, UBUNTU-CVE-2025-11677.