CVE-2026-31789

OpenSSL is widely used to handle digital certificates (the “who are you / is this connection trustworthy” part of many internet connections). This bug can be triggered by a malicious certificate that contains an unusually large piece of certificate data; when OpenSSL converts that data to text in hexadecimal, it may overflow memory on 32-bit systems. That can cause a crash, and in the worst case could let an attacker run code on the server.

This matters if you run software that uses OpenSSL to process X.509 certificates coming from the network. It’s most relevant on 32-bit platforms when your software handles attacker-supplied certificates (for example, during certificate validation or when logging/printing certificate fields). There is no authentication or user action needed for an attacker to try, but the risk is only there if the attacker can reach the certificate-processing code path (network-reachable certificate handling of untrusted certificates).

This is urgent enough to act now because attackers can send specially crafted certificates over the network without needing logins, and the outcome can be a crash or memory corruption. However, public exploit code isn’t known and exploitation requirements are narrow (notably 32-bit platforms and very large certificate fields), so this is an AMBER priority rather than the most critical “red” tier.

Confirm exposure

1. Identify all OpenSSL installations on your systems (including any 32-bit packages/containers). If you have multiple environments (servers, appliances, build images), check each.
2. Determine whether any internet-facing or network-exposed service accepts, validates, or otherwise processes client certificates (X.509) using OpenSSL.
3. Pay special attention to paths that convert certificate fields to text such as logging, monitoring, or diagnostic printing of certificate extensions (for example Subject Key Identifier / Authority Key Identifier).
4. If you find any 32-bit OpenSSL usage and any service that processes untrusted certificates from the network, treat the system as in-scope.

Upgrade to fixed versions

• Update OpenSSL to one of the fixed versions:
  • 3.0.20
  • 3.3.7
  • 3.4.5
  • 3.5.6
  • 3.6.2
• Upgrade carefully in line with your OS/vendor packaging and internal change window.
• After upgrading, confirm your running service is actually linked against/using the updated OpenSSL library (not just that the package is installed).

If you can’t patch immediately

• Reduce exposure by limiting which endpoints/services accept untrusted client certificates from the internet.
• If you can configure certificate logging/printing, consider temporarily disabling verbose certificate field logging for untrusted inputs.

What to monitor

• Look for service crashes/restarts and unusual certificate parsing/logging activity around client certificate handling.
• Monitor for repeated failures from the same source IPs attempting to trigger certificate parsing behavior.

Notes from the issue

• The findings indicate the affected behavior is on 32-bit platforms.
• FIPS modules in OpenSSL 3.6/3.5/3.4/3.3/3.0 are noted as not affected because the code is outside the FIPS module boundary (your exact configuration still determines what’s in use).

Severity and status: Public KEV listing was not found, and there is no public exploit code on record. The traffic-light verdict for this CVE is AMBER.

Mechanism: A heap buffer overflow (CWE-787) occurs when OpenSSL converts an excessively large OCTET STRING from X.509 certificate extensions into a hexadecimal string. On 32-bit platforms, the buffer sizing can overflow due to length multiplication behavior, causing allocation of a smaller buffer than required and resulting in memory corruption.

Attack vector and prerequisites: Network-reachable attacker supplies a crafted X.509 certificate containing an overly large OCTET STRING in specific extensions such as SKID or AKID. No authentication and no user interaction are required. Exploitation is tied to certificate processing and (per the issue description) can involve code paths that print or log certificate content.

Fix availability: Fixed OpenSSL versions include 3.0.20, 3.3.7, 3.4.5, 3.5.6, and 3.6.2.

Exploit maturity: No public exploit is known; exploitation is not confirmed by KEV in the provided findings. The EPSS prediction is low and flat, but it is not a deciding factor here compared to the AMBER operational risk assessment.