CyberSecBulletin
CVE-2026-53221NVD status: Modified

In the Linux kernel, the following vulnerability has been resolved: ip6_vti: fix incorrect…

Published Updated By the CyberSecBulletin desk

CVE-2026-53221 is a critical-severity improper input validation vulnerability in Linux, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions c327fa4fca31415431202e063767a7ae342e19c6, fc657ac0767c49839b3ef0b08dc0953ca30883f8, 47fb3c2b4203556308e64354b3e78f2ce221d646 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.58% chance of exploitation within 30 days, which is low compared with other CVEs.

Patch this week

Critical severity: a successful attack would have severe impact.

What to do

  1. Update Linux to c327fa4fca31415431202e063767a7ae342e19c6 or fc657ac0767c49839b3ef0b08dc0953ca30883f8 or 47fb3c2b4203556308e64354b3e78f2ce221d646 or f513f308cc4bdb4530d033431592ffbc29b7fca1, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.10.259 or 5.15.210 or 6.1.176 or 6.6.143, whichever matches your release line, or a later version.
  3. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxfbe68ee87522f6eaa10f9076c0a7117e1613f2f7 up to, but not including, c327fa4fca31415431202e063767a7ae342e19c6; fbe68ee87522f6eaa10f9076c0a7117e1613f2f7 up to, but not including, fc657ac0767c49839b3ef0b08dc0953ca30883f8; fbe68ee87522f6eaa10f9076c0a7117e1613f2f7 up to, but not including, 47fb3c2b4203556308e64354b3e78f2ce221d646; fbe68ee87522f6eaa10f9076c0a7117e1613f2f7 up to, but not including, f513f308cc4bdb4530d033431592ffbc29b7fca1; fbe68ee87522f6eaa10f9076c0a7117e1613f2f7 up to, but not including, 90fd4513315ca07da99cfd8549d3e553a7160f0d; fbe68ee87522f6eaa10f9076c0a7117e1613f2f7 up to, but not including, 2abfb19bbb81958714ad1d43ebeb65b30394184b; fbe68ee87522f6eaa10f9076c0a7117e1613f2f7 up to, but not including, 2fc7bc087cc7085368263d9d37bfe9a0bddd6a2d; fbe68ee87522f6eaa10f9076c0a7117e1613f2f7 up to, but not including, a5c0359f5cbc51a2e2b114d6041e0f3c73f903e9; and 1 more rangesc327fa4fca31415431202e063767a7ae342e19c6, fc657ac0767c49839b3ef0b08dc0953ca30883f8, 47fb3c2b4203556308e64354b3e78f2ce221d646, f513f308cc4bdb4530d033431592ffbc29b7fca1, 90fd4513315ca07da99cfd8549d3e553a7160f0d, 2abfb19bbb81958714ad1d43ebeb65b30394184b
SiemensSIMATIC S7-1500 TM MFP - GNU/Linux subsystemall versionsNot stated
LinuxLinux Kernel3.19 up to, but not including, 5.10.259; 5.11 up to, but not including, 5.15.210; 5.16 up to, but not including, 6.1.176; 6.2 up to, but not including, 6.6.143; 6.7 up to, but not including, 6.12.94; 6.13 up to, but not including, 6.18.36; 6.19 up to, but not including, 7.0.13; 7.15.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.94, 6.18.36

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
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
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:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CNA.

Official description

In the Linux kernel, the following vulnerability has been resolved: ip6_vti: fix incorrect tunnel matching in vti6_tnl_lookup() In vti6_tnl_lookup(), when an exact match for a tunnel fails, the code falls back to searching for wildcard tunnels: - Tunnels matching the packet's local address, with any remote address wildcard remote). - Tunnels matching the packet's remote address, with any local address (wildcard local). However, vti6 stores all these different types of tunnels in the same hash table (ip6n->tnls_r_l) prone to hash collisions. The bug is that the fallback search loops in vti6_tnl_lookup() were missing checks to ensure that the candidate tunnel actually has a wildcard address.

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

The underlying weakness: Improper Input Validation

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

How developers prevent this class of flaw

  • Consider using language-theoretic security (LangSec) techniques that characterize inputs using a formal language and build recognizers for that language. This effectively requires parsing to be a distinct layer that effectively enforces a boundary between raw input and internal data representations, instead of allowing parser code to be scattered throughout the program, where it could be subject to errors or inconsistencies that create weaknesses.
  • Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
  • Understand all the potential areas where untrusted inputs can enter the product, including but not limited to: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.

More Improper Input Validation vulnerabilities (CWE-20)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Recent Improper Input Validation vulnerabilities

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