Linux Kernel nexthop net/ipv4/nexthop.c nh_rt_cache_flush use after free

Summaryinfo

A vulnerability has been found in Linux Kernel and classified as very critical. This impacts the function nh_rt_cache_flush of the file net/ipv4/nexthop.c of the component nexthop. This manipulation causes use after free. This vulnerability appears as CVE-2026-74561. The attack may be initiated remotely. There is no available exploit.

Detailsinfo

A vulnerability has been found in Linux Kernel (the affected version unknown) and classified as very critical. Affected by this vulnerability is the function nh_rt_cache_flush of the file net/ipv4/nexthop.c of the component nexthop. The manipulation with an unknown input leads to a use after free vulnerability. The CWE definition for the vulnerability is CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: nexthop: avoid unlocked f6i_list walk in nh_rt_cache_flush nh_rt_cache_flush() walks nh->f6i_list during an RTNL-serialized nexthop replace without holding nh->lock, racing the unlocked IPv6 route add/delete that mutate the list under nh->lock and free fib6_info entries (nh_rt_cache_flush() is inlined into rtm_new_nexthop()): BUG: KASAN: slab-use-after-free in nh_rt_cache_flush (net/ipv4/nexthop.c:2243) Read of size 8 at addr ffff888012953e18 by task exploit/146 nh_rt_cache_flush (net/ipv4/nexthop.c:2243) replace_nexthop (net/ipv4/nexthop.c:2610) rtm_new_nexthop (net/ipv4/nexthop.c:3323) rtnetlink_rcv_msg (net/core/rtnetlink.c:7076) Unlike the other f6i_list walks, this one bumps each route's sernum via fib6_update_sernum_upto_root(), which needs tb6_lock; taking nh->lock around it would invert the established tb6_lock -> nh->lock order and deadlock. As the only purpose is to invalidate cached dsts, bump the IPv6 sernum for the whole netns with rt_genid_bump_ipv6() instead, mirroring the rt_cache_flush() already done for IPv4 just above.

It is possible to read the advisory at git.kernel.org. This vulnerability is known as CVE-2026-74561 since 08/15/2026. The exploitation appears to be easy. The attack can be launched remotely. Additional levels of successful authentication are necessary for exploitation. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 08/15/2026).

Applying the patch 44f53e4331a30fabc38a411fae7524341b618db3/4787a6d2629b4e8c0b6bacab1f75c1660eca44d9 is able to eliminate this problem.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

License

• open-source

Website

• Vendor: https://www.kernel.org/

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