Known exploited vulnerability
CVE-2021-22555
The short answer
CVE-2021-22555 affects n/a Linux Kernel and is rated high (CVSS 7.8). CISA added it to the Known Exploited Vulnerabilities catalog on 2025-10-06: attackers are using it, so patch it first. The vendor has linked a patch.
What it is
A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in net/netfilter/x_tables.c. This allows an attacker to gain privileges or cause a DoS (via heap memory corruption) through user name space
Weakness: CWE-787.
Severity
7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Exploited (CISA KEV)
Yes, since Oct 6, 2025
Federal due date Oct 27, 2025
EPSS, next 30 days
79%
Higher than 100% of scored CVEs
How it can be exploited
- Attack vector
- Local
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- High
What CISA says to do
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Affected products
Linux Kernel. NVD's record lists the exact affected versions.
References
- git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=9fa492cdc160cd27ce1046cb36f47d3b2b1efa21 Mailing ListPatchVendor Advisory
- git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=b29c457a6511435960115c0f548c4360d5f4801d Mailing ListPatchVendor Advisory
- github.com/google/security-research/security/advisories/GHSA-xxx5-8mvq-3528 ExploitThird Party Advisory
- security.netapp.com/advisory/ntap-20210805-0010/ Third Party Advisory
- git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=9fa492cdc160cd27ce1046cb36f47d3b2b1efa21 Mailing ListPatchVendor Advisory
- git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=b29c457a6511435960115c0f548c4360d5f4801d Mailing ListPatchVendor Advisory
- github.com/google/security-research/security/advisories/GHSA-xxx5-8mvq-3528 ExploitThird Party Advisory
- security.netapp.com/advisory/ntap-20210805-0010/ Third Party Advisory
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-22555 US Government Resource
Questions
Is CVE-2021-22555 being exploited?
Yes. CISA added CVE-2021-22555 to its Known Exploited Vulnerabilities catalog on 2025-10-06, with a federal remediation due date of 2025-10-27.
How do I fix 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.
From NVD, CISA KEV, FIRST EPSS and OSV.dev, checked . Status on NVD: Analyzed. The description is NVD's text, quoted as published.
Related
Latest CVEs this week
Critical and High CVEs from the last 7 days, with KEV and EPSS.
Exploited vulnerabilities by vendor
Every vendor in CISA's KEV catalog, with its count.
Linux exploited vulnerabilities
Everything CISA lists as exploited for Linux.
Vulnerability watch
A briefing and a fix pull request when an advisory hits your dependencies.
Know the day a CVE lands in your code
Connect a GitHub repository and ZeusQA checks its dependencies daily, briefs each advisory and opens the fix. Three test runs free, no card.