CVE-2026-53306: tty: hvc_iucv: fix off-by-one in number of supported devices

highCVSS 7.1CVE-2026-53306

CSIRTS triage

Privilege escalation

What: The vulnerability is an off-by-one error in the number of supported devices in the tty: hvc_iucv subsystem.
Who is affected: Deployments using the tty: hvc_iucv subsystem may be affected.
Urgency: Remediation is high urgency due to the high severity rating.
Action: Apply the relevant patches as soon as possible.

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 7.1
Published: 2026-06-09
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-53306

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-2026-533060.12% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 2% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-53306	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

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

Recent advisories for tty

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.

unknownCVE-2026-53306: In the Linux kernel, the following vulnerability has been resolved: tty: hvc_iucv: fix off-by-…nvd · 2026-06-26