CVE-2026-31495 netfilter: ctnetlink: use netlink policy range checks
Improper validation of TCP window scale values in ctnetlink allows undefined behavior via shift operations, potentially causing kernel crashes.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-31495?
CVE-2026-31495 is a medium-severity vulnerability in Linux kernel, published on 22 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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 to ctnetlink for the fixes tree.
Which versions are affected by CVE-2026-31495?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31495?
Apply the vendor's patch.
Is CVE-2026-31495 being exploited?
There is no known exploitation of CVE-2026-31495 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-83303, BELL-CVE-2026-31495, DEBIAN-CVE-2026-31495, GHSA-q87j-mxf4-249g, ROOT-OS-DEBIAN-11-CVE-2026-31495, ROOT-OS-DEBIAN-12-CVE-2026-31495 and 4 more.