CVE-2026-64538 is a vulnerability in Linux Kernel
Published on July 27, 2026
ipv6: Fix null-ptr-deref in fib6_nh_mtu_change().
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
Products Associated with CVE-2026-64538
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Affected Versions
Linux:- Version c0b220cf7d80eb8a36ae9f12cae6df4577a6814e and below d08d019f2f43a6f9a71e81868bbc326b3afaf37b is affected.
- Version c0b220cf7d80eb8a36ae9f12cae6df4577a6814e and below 1451deca9896957159f0666520a792c1b861af4f is affected.
- Version c0b220cf7d80eb8a36ae9f12cae6df4577a6814e and below b2c70dd3326809429b709a9c7e9220d29923051a is affected.
- Version c0b220cf7d80eb8a36ae9f12cae6df4577a6814e and below 302d57ed7872838b40e56a868fb4c7da7da606e9 is affected.
- Version c0b220cf7d80eb8a36ae9f12cae6df4577a6814e and below 80600b5d0f3ecb9324120dc95b5e915130f516c5 is affected.
- Version c0b220cf7d80eb8a36ae9f12cae6df4577a6814e and below b0d0eb13a0441a8ebf4f227843deaf494f1e2c33 is affected.
- Version c0b220cf7d80eb8a36ae9f12cae6df4577a6814e and below 6428634f7a0b7878144b4925c37856bef3224967 is affected.
- Version c0b220cf7d80eb8a36ae9f12cae6df4577a6814e and below 46c3b8191aad3d032776bf3bebf03efdf5f4b905 is affected.
- Version 5.3 is affected.
- Before 5.3 is unaffected.
- Version 5.10.261, <= 5.10.* is unaffected.
- Version 5.15.212, <= 5.15.* is unaffected.
- Version 6.1.178, <= 6.1.* is unaffected.
- Version 6.6.145, <= 6.6.* is unaffected.
- Version 6.12.97, <= 6.12.* is unaffected.
- Version 6.18.40, <= 6.18.* is unaffected.
- Version 7.1.5, <= 7.1.* is unaffected.
- Version 7.2-rc1, <= * is unaffected.