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

highCVSS 7.5CVE-2026-12340

CSIRTS triage

Other

What: An out-of-bounds heap read occurs in the computation of the Subject Key Identifier for SM2/SM3 certificates.
Who is affected: Deployments using SM2/SM3 certificates.
Urgency: Remediation is urgent due to the high severity of the vulnerability, despite no known exploitation.
Action: Update the affected libraries handling SM2/SM3 certificates.

AI-assisted analysis generated from the source advisory — verify against the original.

Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: high — CVSS 7.5
Published: 2026-06-09
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/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 during SM2/SM3 certificate signature verification. When parsing a cert…nvd

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
highCVE-2026-12340: Out-of-bounds heap read during SM2/SM3 certificate signature verification. When parsing a cert…nvd · 2026-06-25
criticalCVE-2026-12087: Socket versions before 2.041 for Perl have an out-of-bounds heap readmsrc · 2026-06-09
unknownCVE-2026-8686 - Heap out-of-bounds read in coreMQTT MQTT5 property parsingaws · 2026-06-05