CVE-2026-64538: 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->

unknownCVE-2026-64538

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

Details

Source: NVD Recent CVEs (US · database · site)
Severity: unknown
Published: 2026-07-27
Last updated: 2026-07-27
Exploitation: Not in CISA KEV at last sync

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-64538

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-645380.18% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 7% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-64538	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

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