CVE-2021-4044

What it is

Internally 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).

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of service disruption.

Exploit odds

50.1% chance of exploitation in the next 30 days (EPSS). Higher than most.

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-12-14 19:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 04:18 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 50.1% in the next 30 days (EPSS).
• Severity: 7.5 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-12-14 19:15 UTC

Last modified

2026-06-17 04:18 UTC

Exploit probability

50.1% · EPSS, next 30 days

Weakness

CWE-835

Record status

Modified

Affected

• OpenSSL < 1.0.2
• OpenSSL 1.1.0
• OpenSSL 3.0.0
• Netapp Cloud Backup
• Netapp e-series Performance Analyzer
• Netapp Ontap Select Deploy Administration Utility
• Netapp Snapcenter
• Netapp a250 Firmware

Attack profile CVSS 3.1 · 7.5

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-4044.md and follow it. Check whether this project is affected by CVE-2021-4044. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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