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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| warmcat | libwebsockets | 3 – ≤ 4.4.1,4.3.6 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | libwebsockets | 4.3.5-3 | — |
| Debian 13 | libwebsockets | 4.3.5-1+deb13u1 | — |
| Debian 12 | libwebsockets | No fix yet | — |
| Debian 11 | libwebsockets | 4.0.20-2+deb11u1 | DLA-4373-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 25.10 | libwebsockets | No fix yet | — |
| Ubuntu 22.04 LTS | libwebsockets | 4.0.20-2ubuntu1.1 | USN-8024-1 |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 24.04 LTS | libwebsockets | 4.3.3-1.1ubuntu0.1~esm1 | USN-8024-1 |
| Ubuntu Pro 20.04 LTS | libwebsockets | 3.2.1-3ubuntu0.1~esm1 | USN-8024-1 |
Advisories 2
- USN-8024-1 libwebsockets vulnerabilities Ubuntu Security Notices (USN) · Apr 27, 2026
- DLA-4373-1 libwebsockets - security update Debian Security (DSA / DLA) · Nov 17, 2025
References
- https://libwebsockets.org/git/libwebsockets/commit?id=2f082ec31261f556969160143ba94875d783971a patch vendor-advisory
- https://www.nozominetworks.com/labs/vulnerability-advisories-cve-2025-11677 third-party-advisory