SARA / Free Tools / KEV / CVE-2021-22555

CVE-2021-22555 on CISA KEV

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 KEV — Actively Exploited

Linux Kernel Heap Out-of-Bounds Write Vulnerability

Vendor / Product
— / Linux / Kernel
Added to KEV
2025-10-06
BOD 22-01 due
2025-10-27
Ransomware use
Unknown
CVSS / EPSS
8.3 HIGH · EPSS 85.24%

01What CISA says about this vulnerability

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

02Required action — verbatim from 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.

03Notes & references

04SARA's analyst layer — why this matters

This vulnerability is currently on the CISA KEV list, which CISA only adds CVEs to when there is reliable evidence of active exploitation in the wild. For federal civilian agencies, BOD 22-01 requires remediation by the due date above. For everyone else, KEV is the strongest "patch immediately" signal you can get from public threat intel.

05Affected products (summary)

VendorProductVersions
na / Linux Kernel2.6.19-rc1

06Detection

Open the Sigma generator with a pre-filled prompt for this CVE to draft a starting detection:

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