CyberSecBulletin
CVE-2021-22555Exploited in the wildNVD status: Analyzed

Linux Kernel Heap Out-of-Bounds Write

Published Updated By the CyberSecBulletin desk

CVE-2021-22555 is a high-severity out-of-bounds write vulnerability in Linux Kernel, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. Affected Linux Kernel versions: 2.6.19-rc1. The record does not name a fixed version, so check the vendor advisory. CISA added it to the Known Exploited Vulnerabilities catalogue on October 6, 2025, which means attacks have been observed in the wild.

Patch now

Attackers are already exploiting this vulnerability, according to CISA.

What to do

  1. Check which version of Linux Kernel you run against the affected versions below, and install the vendor's latest release.
  2. 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.
  3. Read the advisory on git.kernel.org for workarounds and exact fixed builds.

Affected products and versions

VendorProductAffected versionsFixed in
Linux KernelLinux Kernel2.6.19-rc1Not stated
NetAppC400 FirmwareNot specified in the recordNot stated
NetAppC250 FirmwareNot specified in the recordNot stated
NetAppH410c FirmwareNot specified in the recordNot stated
NetAppH300s FirmwareNot specified in the recordNot stated
NetAppH500s FirmwareNot specified in the recordNot stated
NetAppH700s FirmwareNot specified in the recordNot stated
NetAppH410s FirmwareNot specified in the recordNot stated
BroadcomFabric Operating SystemNot specified in the recordNot stated
NetAppFas 8300 FirmwareNot specified in the recordNot stated
NetAppFas 8700 FirmwareNot specified in the recordNot stated
NetAppAff A400 FirmwareNot specified in the recordNot stated
NetAppAff A250 FirmwareNot specified in the recordNot stated
NetAppAff 500f FirmwareNot specified in the recordNot stated
NetAppH610c FirmwareNot specified in the recordNot stated
NetAppH610s FirmwareNot specified in the recordNot stated
NetAppH615c FirmwareNot specified in the recordNot stated
NetAppCloud BackupNot specified in the recordNot stated
NetAppHci Management NodeNot specified in the recordNot stated
NetAppSolidfireNot specified in the recordNot stated
NetAppSolidfire Baseboard Management ControllerNot specified in the recordNot stated

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
LocalThe attacker needs local access or must trick a user into running something.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.18.3HighCNA (google.com)
CVSS 3.17.8HighNVD
CVSS 2.04.6MediumNVD

Official description

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

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Out-of-bounds Write

The product writes data past the end, or before the beginning, of the intended buffer.

How developers prevent this class of flaw

  • Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer. Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.
  • Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Examples include the Safe C String Library (SafeStr) by Messier and Viega, and the Strsafe.h library from Microsoft. These libraries provide safer versions of overflow-prone string-handling functions.
  • Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND discusses canary-based detection in detail.

More Out-of-bounds Write vulnerabilities (CWE-787)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: active, automatable: no, technical impact: total).
  3. Added to CISA's Known Exploited Vulnerabilities catalogue.
  4. Deadline for US federal agencies to remediate, set by CISA.
  5. Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in Linux Kernel

All Linux Kernel vulnerabilities

Recent Out-of-bounds Write vulnerabilities

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