Linux · Kernel
CVE-2021-22555
Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACE
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
CISA: 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.
What 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.
Deadline for US federal agencies: October 27, 2025
- Added to the CISA list
- October 6, 2025
- Published
- July 7, 2021
- Severity
- High 8.3 CVSS 3.1
- Chance of attacks in the next 30 days (EPSS)
- 79% in the top 0.4% of all known vulnerabilities
- Weakness
- CWE-787
- More details
- NVD · CVE.org · CISA
All references (9)
- https://github.com/google/security-research/security/advisories/GHSA-xxx5-8mvq-3528
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=9fa492c…
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=b29c457…
- http://packetstormsecurity.com/files/163528/Linux-Kernel-Netfilter-Heap-Out-Of-Bounds-Write.html
- https://security.netapp.com/advisory/ntap-20210805-0010/
- http://packetstormsecurity.com/files/163878/Kernel-Live-Patch-Security-Notice-LSN-0080-1.html
- http://packetstormsecurity.com/files/164155/Kernel-Live-Patch-Security-Notice-LSN-0081-1.html
- http://packetstormsecurity.com/files/164437/Netfilter-x_tables-Heap-Out-Of-Bounds-Write-Privilege-Escalation.…
- http://packetstormsecurity.com/files/165477/Kernel-Live-Patch-Security-Notice-LSN-0083-1.html
More exploited flaws from Linux
| Added | Vulnerability | Product | Severity | Attack chance |
|---|---|---|---|---|
| Sep 18, 2026 | Improper Check for Unusual or Exceptional Conditions | Kernel | Critical 9.8 | 3.3% |
| Sep 18, 2026 | Race Condition | Kernel | High 7.8 | 1.6% |
| Sep 18, 2026 | Out-of-Bounds Write | Kernel | High 8.8 | 0.9% |
| Aug 27, 2026 | Unspecified | Kernel | High 7.8 | 0.7% |
| Aug 26, 2026 | Out-of-Bounds Write | Kernel | High 7.8 | 8.9% |
| Jun 2, 2026 | Improper Authentication | Kernel | High 7.8 | 5.5% |
| May 1, 2026 | Incorrect Resource Transfer Between Spheres | Kernel | High 7.8 | 98% |
| Jan 26, 2026 | Integer Overflow | Kernel | High 7.8 | 15% |
Sources: Known Exploited Vulnerabilities (CISA, public domain), CVE records (cve.org) and EPSS (FIRST). The chance of attacks is the EPSS estimate that someone will try to exploit the flaw in the next 30 days.