CVE-2026-31789: Heap Buffer Overflow in Hexadecimal Conversion
Vulnerability summary
CVE-2026-31789 is a critical (CVSS 9.8) Out-of-bounds Write vulnerability in openssl. EPSS estimates a 0.24% chance of exploitation in the next 30 days, higher than 15.6% of scored vulnerabilities.
Not severe (CVSS 5.8, local access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 20 · Related 20Timeline
- 07-04-2026PublishedVulnerability first disclosed.
- 12-05-2026Last modifiedVulnerability information updated.
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 metrics
7 scores · 7 sources · 1 version- CVE.orgCNA5.8MediumCVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:HDiffers
- OSV · AlpineEcosystem advisory · calculated9.8CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- OSV · UbuntuEcosystem advisory · calculated5.8MediumCVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:HDiffers
- OSV · DebianEcosystem advisory · calculated9.8CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- OSV · WolfiEcosystem advisory · calculated5.8MediumCVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:HDiffers
- OSV · ChainguardEcosystem advisory · calculated5.8MediumCVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:HDiffers
EPSS trend
Probability
0.24%
Chance of exploitation in the next 30 days
Percentile
16%
Versus all other CVEs
30-day change
Decrease -0.08 pp
From 0.33% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Known conditions: local access, no authentication, user interaction (CVSS vector). Other conditions: not stated in public data.
Chainguard11 products
- libcrypto3< 3.6.2-r0
- libcrypto3-2.34< 3.6.2-r0
- openssl< 3.6.2-r0
- openssl-3.5< 3.5.6-r0
- openssl-3.5-libcrypto< 3.5.6-r0
Ubuntu4 products
- edk2All versions (No fix recorded)
- edk2-hweAll versions (No fix recorded)
- openssl< 3.0.2-0ubuntu1.23 | All versions (No fix recorded) | < 3.0.13-0ubuntu3.9 | < 3.5.3-1ubuntu3.3 | < 3.5.5-1ubuntu3
- openssl-fipsAll versions (No fix recorded) | < 3.0.13-0ubuntu3.12+Fips1
Wolfi2 products
- libcrypto3< 3.6.2-r0
- openssl< 3.6.2-r0
Alpine1 product
- openssl≥ 3.0.0, < 3.3.7-r0 | ≥ 3.0.0, < 3.5.6-r0
Debian1 product
- openssl< 3.0.19-1~deb12u2 | < 3.5.5-1~deb13u2 | < 3.6.2-1
Openssl1 product
- 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 | ≥ 3.6.0, < 3.6.2
6 vendors · 20 products
