Exploited vulnerability · CISA KEV
Yes. CVE-2021-22555, Linux Kernel Heap Out-of-Bounds Write Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 6 Oct 2025, 1552 days after it was published. It affects Linux Kernel. If you run it, CISA's required action is: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Linux Kernel contains a heap out-of-bounds write vulnerability that could allow an attacker to gain privileges or cause a DoS (via heap memory corruption) through user name space.
| Vendor | Linux (32 exploited CVEs in KEV) |
| Product | Kernel |
| Vulnerability | Linux Kernel Heap Out-of-Bounds Write Vulnerability |
| Weakness | CWE-787 |
| Published | 7 Jul 2021 |
| Added to KEV | 6 Oct 2025 |
| Reported by (CNA) |
Yes. CISA added CVE-2021-22555 to the Known Exploited Vulnerabilities catalog on 6 Oct 2025, which means there is reliable evidence of exploitation in the wild.
CISA does not list known ransomware use for it. That can change, and exploitation alone is reason to fix it first.
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Check Linux's advisory for the fixed versions, and if you can't patch quickly, restrict access to the affected Kernel and watch it for signs of compromise.
Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in October 2025 · Linux scorecard · act-now radar.
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