CVE-2021-27884
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 · uneditedWeak JSON Web Token (JWT) signing secret generation in YMFE YApi through 1.9.2 allows recreation of other users' JWT tokens. This occurs because Math.random in Node.js is used.
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 confidenceYApi through 1.9.2 uses Math.random() to generate JWT signing secrets. Since Math.random() is not cryptographically secure and produces predictable output based on internal state, an attacker can reconstruct the secret and forge JWT tokens to impersonate other users.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data<= 1.9.2CVSS 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
- Local
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
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 YApi versionLocate the installed YApi version - check package.json in the YApi installation directory, or access the YApi web interface and look for the version number typically displayed in the footer or about pageAffected if version is 1.9.2 or lower
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Identify JWT secret generation codeSearch the YApi source code for JWT-related files, specifically look in the authentication or middleware directories for code that generates JWT signing secretsAffected if code uses Math.random() to generate the JWT secret
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Examine JWT configurationInspect the JWT configuration file or module where the secret is defined and initialized - look for any secret variable assignment that uses Math.random()Affected if the secret initialization uses Math.random() instead of crypto.randomBytes or crypto.randomInt
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Verify token generation mechanismTrace the token creation flow in the YApi codebase - find where jwt.sign() is called and what secret value is passed to itAffected if the secret passed to jwt.sign() originates from Math.random()
The environment is affected if running YApi version 1.9.2 or lower and the JWT signing secret is generated using Math.random() rather than a cryptographically secure random source.
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 dataReplace Math.random()-based secret generation with cryptographically secure random bytes using Node.js crypto module (crypto.randomBytes or crypto.randomInt), and invalidate existing JWT tokens after deployment.
- Consultation3.0 h
- Implementation4.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,648.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-27884 — 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-2021-27884 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
- No spam, self-promotion, credentials, or personal data