CVE-2021-22555: Linux Kernel Vulnerability

What is CVE-2021-22555?

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.

Impact Analysis

Exploitation Probability (EPSS): 85.2% chance of exploitation in the next 30 days (99th percentile). This places the vulnerability in the highest risk tier — immediate action is critical.

Exploit Availability

Public exploit code or proof-of-concept is available for CVE-2021-22555. This significantly increases the risk of exploitation, as attackers can use or adapt existing exploit code rather than developing their own. A public exploit reference has been identified. Organizations should treat this as an urgent patching priority.

Is CVE-2021-22555 being exploited?

Yes. CVE-2021-22555 is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, restricted to CVEs with confirmed active exploitation in the wild. CISA added this vulnerability on 2025-10-06. Inclusion in KEV triggers the patching mandate under BOD 22-01 for U.S. federal civilian agencies, with a remediation deadline of 2025-10-27. Additionally, public exploit code is available, which lowers the barrier for attackers.

How to fix CVE-2021-22555

Update the Linux kernel to the patched version via your distribution's package manager (apt, yum, dnf). A reboot is typically required after kernel updates. For environments where rebooting is not immediately possible, check if a livepatch/kpatch is available from your distribution vendor. Check the Linux Kernel CVEs page for the specific patch or update. CISA's Known Exploited Vulnerabilities catalog requires U.S. federal agencies to remediate this vulnerability by the due date shown below under Binding Operational Directive 22-01. Private organizations should treat KEV entries as priority-one patches because active exploitation has been confirmed in the wild.

Related Vulnerabilities

Other actively exploited vulnerabilities affecting Kernel:

• CVE-2022-0492 (High 7.8) [same product] — A vulnerability was found in the Linux kernel’s cgroup_release_agent_write in…
• CVE-2026-31431 (High 7.8) [same product] — In the Linux kernel, the following vulnerability has been resolved: crypto…
• CVE-2018-14634 (High 7.8) [same product] — An integer overflow flaw was found in the Linux kernel's create_elf_tables()…
• CVE-2025-38352 (High 7.4) [same product] — In the Linux kernel, the following vulnerability has been…
• CVE-2023-0386 (Unknown N/A) [same product] — Linux Kernel contains an improper ownership management vulnerability, where…

Frequently asked questions

Is CVE-2021-22555 critical?

CVE-2021-22555 has a CVSS 3.1 base score of N/A — Unknown severity. Prioritize based on exposure and the active exploitation signal from the KEV listing. The availability of public exploit code further increases the urgency.

Is CVE-2021-22555 being actively exploited?

Yes — CISA added CVE-2021-22555 to the Known Exploited Vulnerabilities catalog on 2025-10-06. Inclusion in KEV means CISA has confirmed in-the-wild exploitation. Public exploit code has also been identified, making exploitation accessible to a broader range of threat actors.

How do I patch CVE-2021-22555?

Apply the security update from Linux for Kernel. Federal agencies must remediate by 2025-10-27 under BOD 22-01. Refer to the Linux Kernel CVEs for the official patch.

What is the CVSS score for CVE-2021-22555?

CVE-2021-22555 has a CVSS 3.1 base score of N/A, classifying it as Unknown severity.