Critical

OpenSSL heap buffer overflow in X.509 OCTET STRING hexadecimal conversion

IdentifiersCVE-2026-31789CWE-122

CVE-2026-31789 is a heap buffer overflow in OpenSSL affecting the conversion of excessively large ASN.1 OCTET STRING values to hexadecimal strings on 32-bit platforms. When OpenSSL converts certain X.509 certificate extension values, such as Subject Key Identifier (SKID) or Authority Key Identifier (AKID), into hex for printing or logging, the required output buffer size is computed as input_length * 3. On 32-bit systems, that multiplication can overflow for very large attacker-controlled OCTET STRING inputs, causing allocation of an undersized heap buffer followed by out-of-bounds writes during hex conversion. The issue is reachable in applications or services that process and print or log untrusted X.509 certificates. The OpenSSL advisory notes that certificates would need to exceed roughly 1 GB in size for exploitation, making practical reachability uncommon. OpenSSL 3.6, 3.5, 3.4, 3.3, and 3.0 are affected; 1.1.1 and 1.0.2 are not. The FIPS modules in 3.6, 3.5, 3.4, 3.3, and 3.0 are not affected because the vulnerable code lies outside the FIPS module boundary.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation can trigger a heap buffer overflow, leading to process crash, denial of service, memory corruption, and potentially attacker-controlled code execution or other undefined behavior. The vendor assessed the issue as Low severity because exploitation is limited to 32-bit platforms and requires unusually large malicious certificate data, but the memory corruption primitive is still potentially serious where the vulnerable code path is reachable.

Mitigation

If you can’t patch tonight, do this now.

Avoid printing or logging fields from untrusted X.509 certificates unless necessary, especially on 32-bit deployments. Reject or pre-screen abnormally large certificates and certificate extensions before any diagnostic formatting or hex conversion occurs. Prefer 64-bit platforms where possible, as the described integer-overflow-to-heap-overflow condition is specific to 32-bit size calculations. Limit exposure of certificate parsing and logging paths to untrusted input sources.

Remediation

Patch, then assume compromise.

Upgrade OpenSSL to a fixed release for the affected branch. The provided content identifies fixes in OpenSSL 3.6.2, 3.5.6, 3.4.5, 3.3.7, and 3.0.20. Downstream distributions should consume the corresponding patched package updates. If running an unsupported branch, migrate to a supported fixed version.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

OpenSSL Software FoundationOpensslapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

16 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

16 SOURCESView more in app

alpinelinuxNews

Apr 15, 2026

Alpine Linue stable releases 3.20.10, 3.21.7, 3.22.4, 3.23.4 | Alpine Linux

A specific vulnerability in OpenSSL addressed in Alpine Linux stable releases 3.20.10, 3.21.7, 3.22.4, and 3.23.4.

help net securityNews

Apr 8, 2026

OpenSSL 3.6.2 lands with eight CVE fixes - Help Net Security

A heap buffer overflow in hexadecimal conversion in OpenSSL.

cyberthroneNews

Apr 8, 2026

OpenSSL 3.6.2: The Moderate Severity Wave - TheCyberThrone

A heap buffer overflow in OpenSSL hexadecimal conversion functionality that may be exploitable when hex conversion APIs process untrusted input.

openssl libraryNews

Apr 7, 2026

OpenSSL Release Announcement for 3.6.2, 3.5.6, 3.4.5, 3.3.7, 3.0.20, 1.1.1zg and 1.0.2zp | OpenSSL Library

Heap buffer overflow in hexadecimal conversion in OpenSSL.

+1 more in the timeline

What this page doesn’t show

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Exposure mapping

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Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity10