CVE-2026-62389
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 · uneditedws before 8.21.1 contains a memory exhaustion vulnerability in lib/receiver.js where the fragment guard only triggers when fragment count reaches maxFragments, allowing attackers to exhaust memory by sending incomplete fragmented WebSocket messages. Attackers can send a text frame with FIN=0 followed by continuation frames without completing the sequence, causing each fragment to be stored as a separate Buffer object with significant overhead, enabling denial of service through heap exhaustion.
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 · high confidenceThe ws WebSocket library before 8.21.1 has a memory exhaustion vulnerability in lib/receiver.js where the fragment guard only triggers when the fragment count reaches maxFragments. Attackers can send incomplete fragmented WebSocket messages (a text frame with FIN=0 followed by continuation frames without completing the sequence), causing each fragment to be stored as a separate Buffer object with significant overhead, leading to heap exhaustion and 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
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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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Check installed ws package versionRun 'npm list ws' in your project directory, or inspect package.json dependencies, or run 'node -e "console.log(require('ws/package.json').version)"'Affected if The version is lower than 8.21.1 (e.g., 8.21.0, 8.20.0, etc.)
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Confirm WebSocket server usageSearch your codebase for 'new WebSocket.Server' or 'wss.createServer' patterns, or check if your application imports and uses the ws library to handle WebSocket connectionsAffected if Your application runs a WebSocket server using the ws library and the version is below 8.21.1
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Identify incomplete message handlingReview the receiver.js behavior in the ws library - look for code handling the FIN flag in fragmented messages. Check if your server configuration sets maxFragments and whether incomplete sequences (FIN=0 followed by partial continuation frames) are being stored as separate BuffersAffected if Your server accepts WebSocket connections and processes fragmented messages without proper guards against incomplete sequences before reaching maxFragments
You are affected if you run a WebSocket server using ws library version below 8.21.1 and accept fragmented WebSocket messages from untrusted clients.
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.
dbcve · scopedUpgrade ws to version 8.21.1 or later to patch the memory exhaustion vulnerability. Implement connection timeouts and message size limits as defense-in-depth measures.
- Upgrade the ws package to version 8.21.1 or later by running: npm install [email protected]
- Verify the upgrade was successful by checking the installed version: npm list ws
- If using a package-lock.json, run npm install to update the locked version
- Restart the application to load the patched library
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation1.0 h
- Implementation1.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,376.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-62389 — 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-2026-62389 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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