Invalid handling of X509_verify_cert() internal errors in libssl

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2021-4044: 50.10% estimated exploitation activity in the next 30 days; percentile 98.91 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Internally libssl in OpenSSL calls X509verifycert() 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 SSLconnect() or SSLdohandshake()) to not indicate success and a subsequent call to SSLgeterror() to return the value SSLERRORWANTRETRYVERIFY. This return value is only supposed to be returned by OpenSSL if the application has previously called SSLCTXsetcertverifycallback(). Since most applications do not do this the SSLERRORWANTRETRYVERIFY return value from SSLgeterror() 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…

Published by the source

15 Dec 2021, 00:00 UTC

Last modified by the source

9 Nov 2023, 16:44 UTC

Source last checked

26 Oct 2026, 15:37 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-mmjf-f5jw-w72q

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# Patch Next advisory brief: CVE-2021-4044

Advisory: Invalid handling of `X509_verify_cert()` internal errors in libssl
IDs: CVE-2021-4044, GHSA-mmjf-f5jw-w72q
Record: https://patchnext.com/advisories/cve-2021-4044 (revision 1, source checked 26 Oct 2026, 15:37 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: openssl-src 300.0.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io openssl-src: affected >= 300.0.0, < 300.0.4; fixed in 300.0.4

## Suggested inspection (read-only)
- crates.io openssl-src: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on openssl-src.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-mmjf-f5jw-w72q (GitHub-reviewed advisory GHSA-mmjf-f5jw-w72q lists affected ranges: crates.io openssl-src >=300.0.0 <300.0.4)

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