CVE-2026-23200 ipv6: Fix ECMP sibling count mismatch when clearing RTF_ADDRCONF
A logic error in Linux kernel IPv6 routing causes a kernel BUG and system crash when adding static routes with gateways, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-23200?
CVE-2026-23200 is a medium-severity vulnerability in Linux kernel, published on 14 Feb 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ipv6: Fix ECMP sibling count mismatch when clearing RTF_ADDRCONF
syzbot reported a kernel BUG in fib6_add_rt2node() when adding an IPv6 route. [0]
Commit f72514b3c569 ("ipv6: clear RA flags when adding a static route") introduced logic to clear RTF_ADDRCONF from existing routes when a static route with the same nexthop is added. However, this causes a problem when the existing route has a gateway.
When RTF_ADDRCONF is cleared from a route that has a gateway, that route becomes eligible for ECMP, i.e. rt6_qualify_for_ecmp() returns true. The issue is that this route was never added to the fib6_siblings list.
This leads to a mismatch between the following counts:
- The sibling count computed by iterating fib6_next chain, which includes the newly ECMP-eligible route
- The actual siblings in fib6_siblings list, which does not include that route
When a subsequent ECMP route is added, fib6_add_rt2node() hits BUG_ON(sibling->fib6_nsiblings != rt->fib6_nsiblings) because the counts don't match.
Fix this by only clearing RTF_ADDRCONF when the existing route does not have a gateway. Routes without a gateway cannot qualify for ECMP anyway (rt6_qualify_for_ecmp() requires fib_nh_gw_family), so clearing RTF_ADDRCONF on them is safe and matches the original intent of the commit.
[0]: kernel BUG at net/ipv6/ip6_fib.c:1217! Oops: invalid opcode: 0000 [#1] SMP KASAN PTI CPU: 0 UID: 0 PID: 6010 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 RIP: 0010:fib6_add_rt2node+0x3433/0x3470 net/ipv6/ip6_fib.c:1217 [...] Call Trace: <TASK> fib6_add+0x8da/0x18a0 net/ipv6/ip6_fib.c:1532 __ip6_ins_rt net/ipv6/route.c:1351 [inline] ip6_route_add+0xde/0x1b0 net/ipv6/route.c:3946 ipv6_route_ioctl+0x35c/0x480 net/ipv6/route.c:4571 inet6_ioctl+0x219/0x280 net/ipv6/af_inet6.c:577 sock_do_ioctl+0xdc/0x300 net/socket.c:1245 sock_ioctl+0x576/0x790 net/socket.c:1366 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f
Weakness: CWE-476
Which versions are affected by CVE-2026-23200?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-23200?
Apply the vendor's patch.
Is CVE-2026-23200 being exploited?
There is no known exploitation of CVE-2026-23200 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-77808, BELL-CVE-2026-23200, DEBIAN-CVE-2026-23200, GHSA-q4xx-rwj3-jf4m, ROOT-OS-DEBIAN-13-CVE-2026-23200, UBUNTU-CVE-2026-23200.