Linux kernel nexthop race condition leads to useafterfree
CVE-2026-74561 Published on August 15, 2026
nexthop: avoid unlocked f6i_list walk in nh_rt_cache_flush
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.
Products Associated with CVE-2026-74561
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Affected Versions
Linux:- Version 081efd18326e353c6fbfdeff903a83edde953f72 and below 44f53e4331a30fabc38a411fae7524341b618db3 is affected.
- Version 081efd18326e353c6fbfdeff903a83edde953f72 and below 4787a6d2629b4e8c0b6bacab1f75c1660eca44d9 is affected.
- Version 6.16 is affected.
- Before 6.16 is unaffected.
- Version 7.1.8, <= 7.1.* is unaffected.
- Version 7.2-rc6, <= * is unaffected.