PatchSiren

PatchSiren cyber security CVE debrief

CVE-2021-22555 Linux CVE debrief

CVE-2021-22555 is a Linux kernel heap out-of-bounds write vulnerability that CISA has added to its Known Exploited Vulnerabilities catalog. Because KEV status indicates active exploitation risk, affected Linux systems should be prioritized for patching or mitigation, especially where kernel exposure cannot be quickly reduced.

Vendor
Linux
Product
Kernel
CVSS
HIGH 8.3
CISA KEV
Listed
Original CVE published
2025-10-06
Original CVE updated
2025-10-06
Advisory published
2025-10-06
Advisory updated
2025-10-06

Who should care

Linux administrators, endpoint and server security teams, cloud and virtualization operators, and any organization running affected Linux kernel builds should treat this as a high-priority remediation item.

Technical summary

The supplied source corpus identifies the issue as a heap out-of-bounds write in the Linux kernel. CISA’s KEV notes reference kernel fixes in net/netfilter/x_tables.c, along with corroborating advisories and the NVD entry, indicating the vulnerable area is in kernel networking/filtering code.

Defensive priority

Immediate

Recommended defensive actions

  • Apply the vendor-recommended kernel update or mitigation as soon as possible.
  • Verify which Linux kernel versions are deployed across servers, endpoints, appliances, and cloud images, then confirm each is patched or backported.
  • If mitigations are unavailable, follow CISA guidance to discontinue use of the product where practical.
  • For cloud services, follow applicable BOD 22-01 guidance and coordinate remediation with the service provider.
  • Track the CISA KEV due date of 2025-10-27 as the remediation target from the supplied timeline.

Evidence notes

CISA lists CVE-2021-22555 in the Known Exploited Vulnerabilities catalog and provides a required action to apply mitigations per vendor instructions. The source item metadata also points to Linux kernel commit references in net/netfilter/x_tables.c, plus corroborating advisory and database links (Google security research, NetApp, and NVD). The supplied corpus does not include a CVSS score.

Sources and references

Verified primary and authoritative sources

  • CVE-2021-22555 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2021-22555

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2021-22555 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2021-22555

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

  • CISA Known Exploited Vulnerabilities catalog

    Publisher, destination, and source semantics verified

    URL: https://www.cisa.gov/known-exploited-vulnerabilities-catalog

    Cybersecurity and Infrastructure Security Agency - Official CISA catalog of vulnerabilities known to be exploited in the wild.

Supplemental references

  • Source item URL

    Unverified legacy reference

    URL: https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json

    cisa_kev

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.