CVE-2025-11677
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedUse 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceA Use After Free vulnerability exists in the WebSocket handshake server (lws_handshake_server) of the libwebsockets library. When a user provides a callback function handling LWS_CALLBACK_HTTP_CONFIRM_UPGRADE, memory is freed but subsequently accessed, leading to potential denial of service.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- High
- Privileges
- None
- Authentication
- X
- User interaction
- None
- Scope
- X
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify libwebsockets installationSearch for libwebsockets library files (e.g., libwebsockets.so, libwebsockets.a) or check package manager listings (dpkg -l | grep libwebsockets, rpm -qa | grep libwebsockets)Affected if libwebsockets is not installed or not in use
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Determine installed versionRun 'pkg-config --modversion libwebsockets' or check library file version with 'strings libwebsockets.so | grep -i version' or review build configurationAffected if version cannot be determined or is older than the patched release
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Locate application code using LWS_CALLBACK_HTTP_CONFIRM_UPGRADESearch source code for 'LWS_CALLBACK_HTTP_CONFIRM_UPGRADE' string using grep -r 'LWS_CALLBACK_HTTP_CONFIRM_UPGRADE' /path/to/codeAffected if callback LWS_CALLBACK_HTTP_CONFIRM_UPGRADE is registered in the application
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Verify callback implementation accesses freed memoryReview the callback function implementation to confirm it performs memory operations after potential free/cleanup pathsAffected if callback code performs memory access after free operations in the handshake flow
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Check for WebSocket upgrade configurationReview server initialization code for websocket protocol setup and LWS_CALLBACK_HTTP_CONFIRM_UPGRADE registration via callback_protocols or user callbacksAffected if websocket upgrade handling is configured with custom callbacks
User is affected if libwebsockets is in use with LWS_CALLBACK_HTTP_CONFIRM_UPGRADE callback handling, where the callback or library code may access memory after it has been freed during the WebSocket handshake process.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataUpgrade libwebsockets to a patched version if available, or avoid using the LWS_CALLBACK_HTTP_CONFIRM_UPGRADE callback configuration until a fix is released.
- Consultation4.0 h
- Implementation12.0 h
- Testing6.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $7,328.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2025-11677 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2025-11677 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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