How severe is CVE-2026-31789?

CVE-2026-31789 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-31789 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (13th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-31789?

CVE-2026-31789 affects Openssl. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-31789?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2026-31789 have an EU (EUVD) identifier?

Yes. CVE-2026-31789 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-19968.

When was CVE-2026-31789 published?

CVE-2026-31789 was published on 2026-04-07 and last updated on 2026-06-17.

CVE-2026-31789

CVE-2026-31789 is a critical-severity vulnerability in Openssl with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-787.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
EPSS exploit prediction: 0% (13th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-19968
Weakness: CWE-787
Affected product: Openssl
Published: 2026-04-07
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2026-31789?: 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.
How severe is CVE-2026-31789?: CVE-2026-31789 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-31789 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (13th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-31789?: CVE-2026-31789 affects Openssl. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-31789?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2026-31789 have an EU (EUVD) identifier?: Yes. CVE-2026-31789 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-19968.
When was CVE-2026-31789 published?: CVE-2026-31789 was published on 2026-04-07 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*

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Threat intelligence

Threat-intel indicators referencing this CVE:

103.90.227.203 (ipv4-addr)
121.161.242.168 (ipv4-addr)
46.235.42.53 (ipv4-addr)
172.83.83.194 (ipv4-addr)
161.97.123.14 (ipv4-addr)
121.84.147.45 (ipv4-addr)
167.71.60.5 (ipv4-addr)
51.75.149.221 (ipv4-addr)