SM2 Decryption Buffer Overflow

Exploitation

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

CVSS

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

EPSS

• CVE-2021-3711: 87.82% estimated exploitation activity in the next 30 days; percentile 99.76 (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.

In order to decrypt SM2 encrypted data an application is expected to call the API function EVPPKEYdecrypt(). Typically an application will call this function twice. The first time, on entry, the "out" parameter can be NULL and, on exit, the "outlen" parameter is populated with the buffer size required to hold the decrypted plaintext. The application can then allocate a sufficiently sized buffer and call EVPPKEYdecrypt() again, but this time passing a non-NULL value for the "out" parameter. A bug in the implementation of the SM2 decryption code means that the calculation of the buffer size required to hold the plaintext returned by the first call to EVPPKEYdecrypt() can be smaller than the actual size required by the second call. This can lead to a buffer overflow when EVPPKEYdecrypt() is called by the application a second time with a buffer that is too small. A malicious attacker who is able present SM2 content for decryption to an application could cause attacker chosen data to…

Published by the source

24 May 2022, 19:12 UTC

Last modified by the source

24 Jun 2024, 21:22 UTC

Source last checked

26 Oct 2026, 15:38 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-5ww6-px42-wc85

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2021-3711

Advisory: SM2 Decryption Buffer Overflow
IDs: CVE-2021-3711, GHSA-5ww6-px42-wc85
Record: https://patchnext.com/advisories/cve-2021-3711 (revision 1, source checked 26 Oct 2026, 15:38 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: openssl-src 111.16.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io openssl-src: affected < 111.16.0; fixed in 111.16.0

## 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-5ww6-px42-wc85 (GitHub-reviewed advisory GHSA-5ww6-px42-wc85 lists affected ranges: crates.io openssl-src >=0 <111.16.0)

Commands are suggestions: review each one before running it.