CVE-2026-31789: OpenSSL buffer overflow (CVSS 9.8)

Description

Issue summary: Converting an excessively large OCTET STRING value to a hexadecimal string leads to a heap buffer overflow on 32 bit platforms. Impact summary: A heap buffer overflow may lead to a crash or possibly an attacker controlled code execution or other undefined behavior. If an attacker can supply a crafted X.509 certificate with an excessively large OCTET STRING value in extensions such as the Subject Key Identifier (SKID) or Authority Key Identifier (AKID) which are being converted to hex, the size of the buffer needed for the result is calculated as multiplication of the input length by 3. On 32 bit platforms, this multiplication may overflow resulting in the allocation of a smaller buffer and a heap buffer overflow. Applications and services that print or log contents of untrusted X.509 certificates are vulnerable to this issue. As the certificates would have to have sizes of over 1 Gigabyte, printing or logging such certificates is a fairly unlikely operation and only 32 bit platforms are affected, this issue was assigned Low severity. The FIPS modules in 3.6, 3.5, 3.4, 3.3 and 3.0 are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

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

Affected products

OpenSSL≥ 3.0.0 < 3.0.20 · ≥ 3.3.0 < 3.3.7 · ≥ 3.4.0 < 3.4.5 · ≥ 3.5.0 < 3.5.6

Remediation

Fixed in

OpenSSL≥ 3.0.20

Patch & vendor advisories

References

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-31789 being actively exploited?

CVE-2026-31789 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.33%.

How severe is CVE-2026-31789?

CVE-2026-31789 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.33% probability of exploitation.

Which products are affected by CVE-2026-31789?

Affected products include OpenSSL.

How do I fix CVE-2026-31789?

Upgrade affected software to a fixed version, for example OpenSSL 3.0.20 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-31789 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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