CVE-2026-98531 ipv6: sr: enforce exact attribute length for SEG6_ATTR_DST

Not scored Published 18 Oct 2026 Updated 19 Oct 2026

A local attacker can leak uninitialized kernel memory by sending malformed netlink messages, exposing sensitive data.

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-2026-98531?

CVE-2026-98531 is a vulnerability in Linux, published on 18 Oct 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:

ipv6: sr: enforce exact attribute length for SEG6_ATTR_DST

In seg6_genl_policy, SEG6_ATTR_DST is defined with .type = NLA_BINARY and .len = sizeof(struct in6_addr). For NLA_BINARY, .len only enforces the maximum payload length and permits shorter payloads (e.g., 0 bytes). When seg6_genl_set_tunsrc() copies sizeof(struct in6_addr) bytes via kmemdup(val, sizeof(*val), GFP_KERNEL), a short SEG6_ATTR_DST attribute triggers a 16-byte out-of-bounds read past skb->tail into uninitialized skb->head memory, which is stored in sdata->tun_src and leaked back to userspace via SEG6_CMD_GET_TUNSRC.

Switch SEG6_ATTR_DST in seg6_genl_policy to NLA_POLICY_EXACT_LEN(sizeof(struct in6_addr)) so that generic netlink validation rejects any attribute whose length is not exactly sizeof(struct in6_addr) with -ERANGE.

Tested in QEMU against Linux 7.3.0-rc3 by sending a SEG6_CMD_SET_TUNSRC Generic Netlink message with a 0-byte SEG6_ATTR_DST attribute followed by SEG6_CMD_GET_TUNSRC. On the unfixed kernel, SEG6_CMD_SET_TUNSRC succeeds (err = 0) and SEG6_CMD_GET_TUNSRC leaks 16 bytes of uninitialized kernel heap memory (tun_src = 836a61ecc4d25a1042a8d60411cfb378); with this patch applied, SEG6_CMD_SET_TUNSRC is rejected by netlink policy validation with -ERANGE (-34) and tun_src remains zeroed.

Which versions are affected by CVE-2026-98531?

How do I fix CVE-2026-98531?

Apply the vendor's patch.

Is CVE-2026-98531 being exploited?

There is no known exploitation of CVE-2026-98531 in the wild and no public exploit code.

Sources

Also known as AZL-109041, BELL-CVE-2026-98531, DEBIAN-CVE-2026-98531, GHSA-365h-h8v6-r47m, UBUNTU-CVE-2026-98531.