CVE-2026-31789 Heap Buffer Overflow in Hexadecimal Conversion
Heap buffer overflow in OpenSSL on 32-bit platforms allows code execution or crashes when logging large X.509 certificates.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-31789?
CVE-2026-31789 is a medium-severity vulnerability in Openssl Openssl, published on 7 Apr 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-787
Which versions are affected by CVE-2026-31789?
It affects 1 product.
Products include Openssl Openssl.
How do I fix CVE-2026-31789?
Apply the vendor's patch.
Is CVE-2026-31789 being exploited?
There is no known exploitation of CVE-2026-31789 in the wild and no public exploit code.
Other vulnerabilities in Openssl Openssl
Sources
Also known as ALPINE-CVE-2026-31789, AZL-81944, BELL-CVE-2026-31789, CLSA-2026-1786493710, CLSA-2026-1789474528, CLSA-2026-1789474778 and 10 more.