CVE-2021-22555
Published: October 6, 2025
Official Description
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.
CISA KEV Advisory
Linux Kernel Heap Out-of-Bounds Write Vulnerability
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.
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Risk Analysis
The Linux Kernel is vulnerable to a heap out-of-bounds write in the user namespace, which could allow an attacker to gain privileges or cause a Denial of Service. The high EPSS score of 0.85239 indicates a significant likelihood of exploitation.
This vulnerability is actively exploited in the wild and is listed in CISA's KEV catalog. Attackers are leveraging this flaw for privilege escalation or denial of service.
Linux administrators should apply the latest kernel updates to address this heap out-of-bounds write vulnerability. Restrict user namespace creation if not strictly required.
Technical Analysis
CVE-2021-22555 requires local access, meaning attackers must already have a foothold on the target system.
Exploitation requires some privileges, which limits the exposure to scenarios where an attacker has already gained initial access.
CISA has added CVE-2021-22555 to the Known Exploited Vulnerabilities (KEV) catalog, confirming active exploitation in the wild. U.S. federal agencies are required to patch this within the mandated timeframe, and all organizations should treat remediation as urgent.
Affected Vendors & Products
Exploit & PoC Resources
All References (5)
Quick Facts
Recommended Actions
- →Apply vendor patches immediately
- →Monitor CVE-2021-22555 in threat intel feeds
- →Review IDS/IPS signatures for exploitation attempts
- !CISA KEV: Federal agencies must patch per BOD 22-01 timeline
- !Active exploitation confirmed — treat as P1