Bug 2460664 (CVE-2026-31495)

Summary: CVE-2026-31495 kernel: netfilter: ctnetlink: use netlink policy range checks
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's netfilter connection tracking (ctnetlink) component. This vulnerability, related to improper input validation, allows an attacker to provide malformed netlink policy attributes. Specifically, invalid values for TCP window scaling (WSCALE) could lead to undefined behavior within the kernel. This could result in a system crash, causing a Denial of Service (DoS) for affected systems.
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Description OSIDB Bzimport 2026-04-22 15:04:01 UTC 
In the Linux kernel, the following vulnerability has been resolved:

netfilter: ctnetlink: use netlink policy range checks

Replace manual range and mask validations with netlink policy
annotations in ctnetlink code paths, so that the netlink core rejects
invalid values early and can generate extack errors.

- CTA_PROTOINFO_TCP_STATE: reject values > TCP_CONNTRACK_SYN_SENT2 at
  policy level, removing the manual >= TCP_CONNTRACK_MAX check.
- CTA_PROTOINFO_TCP_WSCALE_ORIGINAL/REPLY: reject values > TCP_MAX_WSCALE
  (14). The normal TCP option parsing path already clamps to this value,
  but the ctnetlink path accepted 0-255, causing undefined behavior when
  used as a u32 shift count.
- CTA_FILTER_ORIG_FLAGS/REPLY_FLAGS: use NLA_POLICY_MASK with
  CTA_FILTER_F_ALL, removing the manual mask checks.
- CTA_EXPECT_FLAGS: use NLA_POLICY_MASK with NF_CT_EXPECT_MASK, adding
  a new mask define grouping all valid expect flags.

Extracted from a broader nf-next patch by Florian Westphal, scoped to
ctnetlink for the fixes tree.
Comment 1 Keith Grant 2026-04-22 19:12:40 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026042203-CVE-2026-31495-f86b@gregkh/T