CVE-2026-12340: Out-of-bounds heap read during SM2/SM3 certificate signature verification. When parsing a certificate with an SM3wSM2 signature, the Subject Key Identifier computation reads the tr

highCVSS 7.5CVE-2026-12340

Out-of-bounds heap read during SM2/SM3 certificate signature verification. When parsing a certificate with an SM3wSM2 signature, the Subject Key Identifier computation reads the trailing 65 bytes of the public key without checking that the key is at least that long. A public key shorter than 65 bytes results in an out-of-bounds heap read, leading to a potential crash (denial of service); there is no out-of-bounds write. Note this only affects builds with SM2 support (--enable-sm2 or --enable-all).

Details

Source: NVD Recent CVEs (US · database · site)
Severity: high — CVSS 7.5
Published: 2026-06-25
Last updated: 2026-06-26
Exploitation: Not in CISA KEV at last sync

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-12340

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-123400.23% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 13% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-12340	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

highCVE-2026-12340: Out-of-bounds heap read in SM2/SM3 certificate Subject Key Identifier computationmsrc

Recent advisories for Out-of-bounds heap read

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

highCVE-2026-13705: Imager versions before 1.032 for Perl have a heap out-of-bounds read in the bundled Imager::Fi…nvd · 2026-07-06
criticalCVE-2026-56015: Net::IP::LPM versions through 1.10 for Perl allow a heap out-of-bounds read via an unbounded p…nvd · 2026-07-03
lowCVE-2026-56361: ImageMagick before 7.1.2-19 contains an off-by-one error in morphology validation allowing out…nvd · 2026-06-30
criticalCVE-2026-12087: Socket versions before 2.041 for Perl have an out-of-bounds heap readmsrc · 2026-06-09
highCVE-2026-12340: Out-of-bounds heap read in SM2/SM3 certificate Subject Key Identifier computationmsrc · 2026-06-09
unknownCVE-2026-8686 - Heap out-of-bounds read in coreMQTT MQTT5 property parsingaws · 2026-06-05