Linux Kernel up to 7.1.7/7.2-rc5 Nexthop net/ipv6/route.c fib6_check_nh_list/__nexthop_replace_notify lock use after free

Summaryinfo

A vulnerability identified as very critical has been detected in Linux Kernel up to 7.1.7/7.2-rc5. This issue affects the function fib6_check_nh_list/__nexthop_replace_notify of the file net/ipv6/route.c of the component Nexthop. This manipulation of the argument lock causes use after free. The identification of this vulnerability is CVE-2026-74562. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability classified as very critical was found in Linux Kernel up to 7.1.7/7.2-rc5. Affected by this vulnerability is the function fib6_check_nh_list/__nexthop_replace_notify of the file net/ipv6/route.c of the component Nexthop. The manipulation of the argument lock 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: 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.

The advisory is shared at git.kernel.org. This vulnerability is known as CVE-2026-74562 since 08/15/2026. The exploitation appears to be easy. The attack can be launched remotely. Additional levels of successful authentication are needed for exploitation. Technical details are known, but no exploit is available. The price for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 08/15/2026).

Upgrading to version 7.1.8 or 7.2-rc6 eliminates this vulnerability. Applying the patch bb2b072c619c1f741a6234257050f72005dc63ef/072cd1f21819dedd2252e704d255de3b0cfc61a7 is able to eliminate this problem.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.1.0
• 7.1.1
• 7.1.2
• 7.1.3
• 7.1.4
• 7.1.5
• 7.1.6
• 7.1.7
• 7.2-rc1
• 7.2-rc2
• 7.2-rc3
• 7.2-rc4
• 7.2-rc5

License

• open-source

Website

• Vendor: https://www.kernel.org/

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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