CVE-2026-31495

/// Technical description

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

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References