OpenSSLFramework / library
CVE-2021-4044
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 · uneditedInternally libssl in OpenSSL calls X509_verify_cert() on the client side to verify a certificate supplied by a server. That function may return a negative return value to indicate an internal error (for example out of memory). Such a negative return value is mishandled by OpenSSL and will cause an IO function (such as SSL_connect() or SSL_do_handshake()) to not indicate success and a subsequent call to SSL_get_error() to return the value SSL_ERROR_WANT_RETRY_VERIFY. This return value is only supposed to be returned by OpenSSL if the application has previously called SSL_CTX_set_cert_verify_callback(). Since most applications do not do this the SSL_ERROR_WANT_RETRY_VERIFY return value from SSL_get_error() will be totally unexpected and applications may not behave correctly as a result. The exact behaviour will depend on the application but it could result in crashes, infinite loops or other similar incorrect responses. This issue is made more serious in combination with a separate bug in OpenSSL 3.0 that will cause X509_verify_cert() to indicate an internal error when processing a certificate chain. This will occur where a certificate does not include the Subject Alternative Name extension but where a Certificate Authority has enforced name constraints. This issue can occur even with valid chains. By combining the two issues an attacker could induce incorrect, application dependent behaviour. Fixed in OpenSSL 3.0.1 (Affected 3.0.0).
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 confidenceOpenSSL has a flaw where X509_verify_cert() mishandles negative return values, causing SSL functions to incorrectly return SSL_ERROR_WANT_RETRY_VERIFY when applications have not set a cert verify callback. Combined with a separate bug in OpenSSL 3.0 causing false internal errors for certificates without SAN extensions under CA-enforced name constraints, attackers can cause applications to crash, hang, or behave incorrectly.
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
OpenSSLFramework / library
< 1.0.2= 1.1.0= 3.0.0
Node.jsApplication
>= 17.0.0, < 17.3.0all versionsall versionsall versionsall versionsall versionsall versionsCVSS 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 OpenSSL versionRun `openssl version` or check the OpenSSL library file version in your systemAffected if The version is 1.1.0, 3.0.0, or lower than 1.0.2 (note: versions 1.0.2 and below are also end-of-life)
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Check Node.js version if applicableRun `node --version` to determine the Node.js runtime versionAffected if Node.js version is 17.0.0 through 17.2.x (inclusive)
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Identify applications using OpenSSL SSL/TLSReview application dependencies and running processes that link to the affected OpenSSL library using commands like `ldd` or checking package dependenciesAffected if Applications link to OpenSSL 1.1.0 or 3.0.0 and perform certificate verification
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Check if custom certificate verify callback is setReview application code or configuration for calls to SSL_CTX_set_verify or SSL_set_verify functions that register a custom verify callbackAffected if The application does NOT set a custom certificate verification callback (relies on default OpenSSL behavior)
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Check for certificate chains without SAN extensionsInspect certificates in use with `openssl x509 -in cert.pem -text -noout` looking for the Subject Alternative Name fieldAffected if Certificates in the chain lack SAN extensions and are used under CA-enforced name constraints (relevant for OpenSSL 3.0.0)
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Monitor for SSL_ERROR_WANT_RETRY_VERIFY errorsEnable SSL debugging via SSL_CTX_set_debug or application logging, or monitor for abnormal application behavior during TLS handshakesAffected if Applications exhibit crashes, hangs, or report SSL_ERROR_WANT_RETRY_VERIFY unexpectedly during certificate verification
You are affected if your environment uses OpenSSL 1.1.0 or 3.0.0 (or Node.js 17.0.0-17.2.x) AND performs certificate verification without a custom callback, especially with certificates lacking SAN extensions under CA constraints.
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 data1.0.217.3.0
Upgrade to OpenSSL 3.0.1 or later to remediate this vulnerability.
Fix this in OpenSSL
Scoped from the published advisory
- Consultation3.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA3.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,416.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-4044 — 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-2021-4044 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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- Version or environment caveats, and links to real fixes
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