CVE-2021-22555 — Linux Kernel Heap Out-of-Bounds Write Vulnerability

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

• Documented patch — git.kernel.org (NIST National Vulnerability Database)
• Documented patch — git.kernel.org (NIST National Vulnerability Database)

CISA required action CISA

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

US federal deadline: Oct 27, 2025 — passed 353 day(s) ago

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

1. Identify exposed assets running the affected vendor/product/version combinations (Broadcom Fabric Operating System, Linux Linux Kernel, Netapp Aff 500f Firmware…).
2. Treat as emergency remediation: the CVE is in CISA KEV (confirmed exploitation).
3. Apply the fixed version or the patch documented under Remediation.
4. EPSS ahead of 100% of scored CVEs: prioritize it in the patch queue.
5. Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-787 · Out-of-bounds Write

Other CVEs with this weakness →

CISA KEV details CISA

CISA lists a CVE once it has evidence of exploitation against real targets.

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a reference date.

Public exploits, PoCs and detection templates

Public code that demonstrates or tests the flaw raises the odds of mass exploitation — and Nuclei templates help find vulnerable assets in your environment.

Warning: public PoCs are sometimes disguised malware. Use them only for authorized testing in an isolated environment. This portal does not host exploit code — it only points to the sources.

EPSS over time FIRST

Oct 12, 2026 → Oct 14, 2026 · 3 reading(s) · max 78.68%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

• Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
• Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.
• Hunt retroactively in logs from before Oct 6, 2025 (KEV listing): exploitation may have started earlier.

Timeline

What happened to this CVE, newest first.

• 2026
• Affected products removed · 1
  Oct 13, 2026 · NIST National Vulnerability Database
• Affected products added · broadcom/fabric operating system
  Oct 13, 2026 · NIST National Vulnerability Database
• Fix documented
  Oct 13, 2026 · NIST National Vulnerability Database
• Affected products added · netapp/c400 firmware, netapp/c250 firmware, netapp/h410c firmware, netapp/h300s firmware, netapp/h500s firmware, netapp/
  Oct 13, 2026 · NIST National Vulnerability Database
• CVSS changed · 8.3 → 7.8
  Oct 13, 2026 · NIST National Vulnerability Database
• Source status changed · Published → Analyzed
  Oct 13, 2026 · NIST National Vulnerability Database
• Record published
  Oct 13, 2026
• CVSS changed · 8.3
  Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
• Source status changed · → Published
  Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
• SSVC assessment updated
  Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
• Added to CISA KEV (detected)
  Oct 13, 2026 · CISA Known Exploited Vulnerabilities
• Record created in this database
  Oct 13, 2026 · CISA Known Exploited Vulnerabilities
• 2025
• Added to CISA KEV catalog
  Oct 5, 2025 · CISA
• 2021
• CVE published
  Jul 7, 2021 · Google

Source activity

Repeated readings are counted rather than listed.

• 2× References added · Oct 13, 2026 – Oct 13, 2026
• 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

10 on the record

• git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_ta
  x_refsource_MISC, Mailing List, Patch, Vendor Advisory, CVE Program (cve.org) e CISA ADP
• git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_ta
  x_refsource_MISC, Mailing List, Patch, Vendor Advisory, CVE Program (cve.org) e CISA ADP
• www.cisa.gov/known-exploited-vulnerabilities-catalog
  US Government Resource, NIST National Vulnerability Database
• packetstormsecurity.com/files/163878/Kernel-Live-Patch-Security-Notice-LSN-0080-1.html
  x_refsource_MISC, Exploit, Third Party Advisory, VDB Entry, CVE Program (cve.org) e CISA ADP
• security.netapp.com/advisory/ntap-20210805-0010/
  x_refsource_CONFIRM, Third Party Advisory, CVE Program (cve.org) e CISA ADP
• packetstormsecurity.com/files/164155/Kernel-Live-Patch-Security-Notice-LSN-0081-1.html
  x_refsource_MISC, Exploit, Third Party Advisory, VDB Entry, CVE Program (cve.org) e CISA ADP
• packetstormsecurity.com/files/165477/Kernel-Live-Patch-Security-Notice-LSN-0083-1.html
  x_refsource_MISC, Exploit, Third Party Advisory, VDB Entry, CVE Program (cve.org) e CISA ADP
• packetstormsecurity.com/files/164437/Netfilter-x_tables-Heap-Out-Of-Bounds-Write-Privilege-Es
  x_refsource_MISC, Exploit, Third Party Advisory, VDB Entry, CVE Program (cve.org) e CISA ADP
• packetstormsecurity.com/files/163528/Linux-Kernel-Netfilter-Heap-Out-Of-Bounds-Write.html
  x_refsource_MISC, Third Party Advisory, VDB Entry, CVE Program (cve.org) e CISA ADP
• github.com/google/security-research/security/advisories/GHSA-xxx5-8mvq-3528
  x_refsource_MISC, Exploit, Third Party Advisory, CVE Program (cve.org) e CISA ADP

Elsewhere on this site

Related CVEs (same products)

• High CVE-2026-94577 A privilege escalation vulnerability exists in the internal Command-Line Interface (CLI)... 7d
• High CVE-2026-94579 An OS command injection vulnerability exists in the PAM (Pluggable Authentication Module) session... 7d
• High CVE-2026-94585 An authentication bypass vulnerability exists in the web management interface of Brocade Fabric... 7d
• Medium CVE-2026-94581 An OS command injection vulnerability exists in the REST API management interface of Brocade... 7d
• Medium CVE-2026-94586 A command injection vulnerability exists in the WebTools administrative interface handling... 7d
• Medium CVE-2026-94587 A buffer overflow vulnerability exists in the WebTools administrative interface handling... 7d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

• No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
• No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
• No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2021-22555 is "Linux Kernel Heap Out-of-Bounds Write Vulnerability", rated High. It affects Fabric Operating System (Broadcom); versions are in the scope table. It is in CISA KEV: there is evidence of real-world exploitation. CVSS 7.8 describes technical severity. EPSS 78.68% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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