CVE-2021-22555: in the CISA KEV catalogue
Linux Kernel Heap Out-of-Bounds Write Vulnerability. CISA added CVE-2021-22555 to the Known Exploited Vulnerabilities catalogue on 2025-10-06 with a default due date of 2025-10-27. Known ransomware campaign use: Unknown. Forensic triage flag: No.
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. (CISA description)
- Vendor / product
- Linux Kernel
- CWE
- CWE-787
- CISA required action
- Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
- EPSS
- 79%, percentile 99 (scored 2026-11-03)
EPSS puts about 79 in 100 odds (79%) on exploitation activity being observed in the next 30 days. Its score is higher than or equal to that of 99% of scored CVEs. This is a model estimate about exploitation anywhere, not about your environment.
Vendor and reference links (from CISA)
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=9fa492cdc160cd27ce1046cb36f47d3b2b1efa21
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=b29c457a6511435960115c0f548c4360d5f4801d
- https://security.netapp.com/advisory/ntap-20210805-0010/
- https://github.com/google/security-research/security/advisories/GHSA-xxx5-8mvq-3528
- https://nvd.nist.gov/vuln/detail/CVE-2021-22555
Your own deadline under CISA BOD 26-04 depends on exposure, automatability and technical impact: work it out with the BOD 26-04 calculator.
Frequently asked questions
Is CVE-2021-22555 in the CISA KEV catalogue?
Yes. CISA added CVE-2021-22555 (Linux Kernel Heap Out-of-Bounds Write Vulnerability) to the Known Exploited Vulnerabilities catalogue on 2025-10-06. CISA's default due date for it is 2025-10-27.
Is CVE-2021-22555 used in ransomware attacks?
CISA marks known ransomware campaign use as Unknown for CVE-2021-22555. That means CISA lacks confirmation, not that ransomware groups do not use it.
What should I do about CVE-2021-22555?
CISA's required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Sources
- CISA, Known Exploited Vulnerabilities Catalog (accessed 2026-11-03)
- FIRST, Exploit Prediction Scoring System (EPSS) (EPSS by FIRST; scores generated by Empirical Security)
- NVD record for CVE-2021-22555