Heap overflow via overflowing hexadecimal buffer calculation
Published Apr 7, 2026 · Updated Apr 7, 2026
Heap buffer overflow in OpenSSL allows attackers to crash 32-bit applications that print or log crafted X.509 certificates. The crypto/o_str.c buf2hex conversion multiplies the OCTET STRING length by three without first bounding it, so the size wraps and allocation is too small. Reachability requires a certificate over 1 GB to be printed or logged on a 32-bit platform; the affected code is outside the FIPS module boundary.
Summary
What happened
Heap buffer overflow in OpenSSL allows attackers to crash 32-bit applications that print or log crafted X.509 certificates. The crypto/o_str.c buf2hex conversion multiplies the OCTET STRING length by three without first bounding it, so the size wraps and allocation is too small. Reachability requires a certificate over 1 GB to be printed or logged on a 32-bit platform; the affected code is outside the FIPS module boundary.
The record
- CVE
- CVE-2026-31789
- Published
- Apr 7, 2026
- Updated
- Apr 7, 2026
- Vendor
- OpenSSL Project
- Product
- OpenSSL
- Classifications
- CWE-787
- Attack vector
- local
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 7, 2026CVE publishedPublication date reported by the CVE source.
- Apr 7, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=3.0.0 <3.0.20
- Affected versionversion=3.3.0 <3.3.7
- Affected versionversion=3.4.0 <3.4.5
- Affected versionversion=3.5.0 <3.5.6
- Affected versionversion=3.6.0 <3.6.2
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo