Bug 2517094 (CVE-2026-74562)

Summary: CVE-2026-74562 kernel: nexthop: take nh->lock for f6i_list walks in replace check and notify
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Doc Text:
A flaw was found in the Linux kernel's nexthop component. A race condition exists where internal lists are walked without proper locking during nexthop replacement and route deletion. A local attacker could exploit this by concurrently manipulating IPv6 routes, leading to a use-after-free vulnerability. This could result in a system crash, causing a denial of service.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-08-15 12:50:02 UTC 
In the Linux kernel, the following vulnerability has been resolved:

nexthop: take nh->lock for f6i_list walks in replace check and notify

fib6_check_nh_list() and __nexthop_replace_notify() walk nh->f6i_list
during an RTNL-serialized nexthop replace without holding nh->lock. IPv6
RTM_NEWROUTE/RTM_DELROUTE run without RTNL and mutate that list under
nh->lock (fib6_add_rt2node_nh(), fib6_purge_rt()), so both walks race a
concurrent route delete that unlinks and frees a fib6_info:

  BUG: KASAN: slab-use-after-free in rt6_fill_node.isra.0 (net/ipv6/route.c:5799)
  Read of size 4 at addr ffff888014607e64 by task exploit/143
   rt6_fill_node.isra.0 (net/ipv6/route.c:5799)
   fib6_rt_update (net/ipv6/route.c:6412)
   __nexthop_replace_notify (net/ipv4/nexthop.c:2542)
   rtm_new_nexthop (net/ipv4/nexthop.c:2554)
   rtnetlink_rcv_msg (net/core/rtnetlink.c:7076)

  BUG: KASAN: slab-use-after-free in fib6_check_nh_list (net/ipv4/nexthop.c:1605)
  Read of size 8 at addr ffff888014a7d068 by task exploit/142
   fib6_check_nh_list (net/ipv4/nexthop.c:1605)
   rtm_new_nexthop (net/ipv4/nexthop.c:2575)
   rtnetlink_rcv_msg (net/core/rtnetlink.c:7076)

Both walks only read the entries and take no tb6_lock, so protect them
with nh->lock; fib6_rt_update() uses gfp_any(), which returns GFP_ATOMIC
under the lock.
Comment 1 TEJ RATHI 2026-08-17 12:02:56 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081552-CVE-2026-74562-990d@gregkh/T