CVE-2026-64538 ipv6: Fix null-ptr-deref in fib6_nh_mtu_change().
A null pointer dereference in the Linux kernel IPv6 stack allows remote attackers to cause a denial of service via crafted Router Advertisement packets.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-64538?
CVE-2026-64538 is a vulnerability in Linux, published on 27 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ipv6: Fix null-ptr-deref in fib6_nh_mtu_change().
fib6_nh_mtu_change() re-fetches idev via __in6_dev_get(arg->dev) and dereferences idev->cnf.mtu6 without a NULL check. addrconf_ifdown() clears dev->ip6_ptr with RCU_INIT_POINTER() after rt6_disable_ip() has released tb6_lock, so the RA-driven MTU walk can observe a NULL idev and oops. The caller rt6_mtu_change_route() guards its own __in6_dev_get(), but this re-fetch is unguarded; nexthop-backed routes survive addrconf_ifdown()'s flush, so the walk still reaches it after ip6_ptr is nulled.
Return 0 when idev is NULL, matching rt6_mtu_change_route() and the fib6_mtu() fix in commit 5ad509c1fdad ("ipv6: Fix null-ptr-deref in fib6_mtu().").
Oops: general protection fault, ... KASAN: null-ptr-deref in range [0x00000000000002a8-0x00000000000002af] RIP: 0010:fib6_nh_mtu_change+0x203/0x990 rt6_mtu_change_route+0x141/0x1d0 __fib6_clean_all+0xd0/0x160 rt6_mtu_change+0xb4/0x100 ndisc_router_discovery+0x24b5/0x2cb0 icmpv6_rcv+0x12e9/0x1710 ipv6_rcv+0x39b/0x410
Which versions are affected by CVE-2026-64538?
How do I fix CVE-2026-64538?
Apply the vendor's patch.
Is CVE-2026-64538 being exploited?
There is no known exploitation of CVE-2026-64538 in the wild and no public exploit code.
Sources
Also known as AZL-94050, BELL-CVE-2026-64538, DEBIAN-CVE-2026-64538, GHSA-c37c-frr8-rx54, UBUNTU-CVE-2026-64538.