dbcve.org
Memory Buffer Bounds ErrorWeakness · CWE-119

CVE-2025-1866

CRITICAL · 10.0 CVSS v4.0 Published 2025-03-03
Patch available
A vendor patch is available. No clean upgrade release — apply the published patch.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click Patch available

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 · unedited
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.

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 confidence

A buffer bounds vulnerability in libwebsockets on Win32 platforms allows pointer manipulation leading to out-of-bounds memory access. The flaw exists in code paths only compiled when either LWS_WITHOUT_EXTENSIONS is disabled or LWS_WITH_HTTP_STREAM_COMPRESSION is enabled during build, potentially enabling memory corruption.

MitigationUpgrade to libwebsockets 4.3.4 or later, or ensure affected build configurations are not used. Organizations using the vulnerable configurations should prioritize patching.

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
Low
Privileges
None
Authentication
X
User interaction
None
Scope
X

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/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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify libwebsockets installation
    Search for libwebsockets DLL or shared library files on the system. Common paths on Windows: C:\Program Files\libwebsockets\, or within application directories. Check for files named libwebsockets.dll, websockets.dll, or equivalent.
    Affected if libwebsockets library files are found on a Windows system
  2. Determine installed version
    Inspect the version resource of the DLL file (right-click > Properties > Details), or run: lws --version if the command-line tool is installed. Compare against the fixed version 4.3.4.
    Affected if Installed version is lower than 4.3.4
  3. Inspect build configuration flags
    If libwebsockets was built from source, review the build configuration or CMakeCache.txt for LWS_WITHOUT_EXTENSIONS and LWS_WITH_HTTP_STREAM_COMPRESSION settings. Check if the library was compiled with extension support enabled or HTTP compression enabled.
    Affected if LWS_WITHOUT_EXTENSIONS is set to OFF (disabled) OR LWS_WITH_HTTP_STREAM_COMPRESSION is set to ON (enabled) in the build configuration
  4. Confirm Windows platform
    Verify the operating system is a Windows variant (Win32). The vulnerability specifically affects Win32 platform code paths.
    Affected if Running on Windows (Win32) platform

A user is affected if libwebsockets version is below 4.3.4 on Windows with either LWS_WITHOUT_EXTENSIONS disabled or LWS_WITH_HTTP_STREAM_COMPRESSION enabled in the build configuration.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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.

dbcve · scoped
Patch available Apply the vendor patch
Vendor patch github.com →
Interim mitigation

Upgrade to libwebsockets 4.3.4 or later, or ensure affected build configurations are not used. Organizations using the vulnerable configurations should prioritize patching.

Recommended fix High confidence

libwebsockets 4.3.4

  1. 1. Identify the current version of libwebsockets in use
  2. 2. Download or obtain libwebsockets version 4.3.4 or later from the official repository (github.com/warmcat/libwebsockets)
  3. 3. Rebuild and deploy the new version, replacing the vulnerable installation
  4. 4. Alternatively, if upgrading is not immediately feasible, ensure CMake build options remain at defaults: LWS_WITHOUT_EXTENSIONS=ON and LWS_WITH_HTTP_STREAM_COMPRESSION=OFF to avoid compiling the vulnerable code path

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
Get the patch applied

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,120.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2025-1866 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-1866 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • 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
  • No spam, self-promotion, credentials, or personal data