{"id":"CVE-2026-23200","title":"ipv6: Fix ECMP sibling count mismatch when clearing RTF_ADDRCONF","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nipv6: Fix ECMP sibling count mismatch when clearing RTF_ADDRCONF\n\nsyzbot reported a kernel BUG in fib6_add_rt2node() when adding an IPv6\nroute. [0]\n\nCommit f72514b3c569…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= cb2b0caa8ca93cbe39177516669bf699c74f7041 < 50b7c7a255858a85c4636a1e990ca04591153dca","Linux >= 03f642caab84bbfd138e74f671bb436186ea7e82 < d8143c54ceeba232dc8a13aa0afa14a44b371d93","Linux >= 3e5b25da0b4109a3e063759735e6ec4236ea5a05 < b8ad2d53f706aeea833d23d45c0758398fede580","Linux >= f72514b3c5698e4b900b25345e09f9ed33123de6 < bbf4a17ad9ffc4e3d7ec13d73ecd59dea149ed25","Linux 61d88ea0f30c88e4ea98793594943aed8f1fc9ab","Linux >= 6.17.13 < 6.18","Linux >= 6.6.120 < 6.6.124","Linux >= 6.12.63 < 6.12.70","Linux >= 6.18.2 < 6.18.10"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-11-05T21:22:11.025337Z"},"published":"2026-02-14","updated":"2026-11-05","sourceUpdated":"2026-11-05T21:23:21.838Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-23200","references":[{"url":"https://git.kernel.org/stable/c/50b7c7a255858a85c4636a1e990ca04591153dca"},{"url":"https://git.kernel.org/stable/c/d8143c54ceeba232dc8a13aa0afa14a44b371d93"},{"url":"https://git.kernel.org/stable/c/b8ad2d53f706aeea833d23d45c0758398fede580"},{"url":"https://git.kernel.org/stable/c/bbf4a17ad9ffc4e3d7ec13d73ecd59dea149ed25"}],"tags":["cve.org"],"epss":0.00133,"epssPercentile":0.02865,"ingestedAt":"2026-11-05T22:38:32.086Z","slug":"CVE-2026-23200","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nipv6: Fix ECMP sibling count mismatch when clearing RTF_ADDRCONF\n\nsyzbot reported a kernel BUG in fib6_add_rt2node() when adding an IPv6\nroute. [0]\n\nCommit f72514b3c569 (\"ipv6: clear RA flags when adding a static\nroute\") introduced logic to clear RTF_ADDRCONF from existing routes\nwhen a static route with the same nexthop is added. However, this\ncauses a problem when the existing route has a gateway.\n\nWhen RTF_ADDRCONF is cleared from a route that has a gateway, that\nroute becomes eligible for ECMP, i.e. rt6_qualify_for_ecmp() returns\ntrue. The issue is that this route was never added to the\nfib6_siblings list.\n\nThis leads to a mismatch between the following counts:\n\n- The sibling count computed by iterating fib6_next chain, which\n  includes the newly ECMP-eligible route\n\n- The actual siblings in fib6_siblings list, which does not include\n  that route\n\nWhen a subsequent ECMP route is added, fib6_add_rt2node() hits\nBUG_ON(sibling->fib6_nsiblings != rt->fib6_nsiblings) because the\ncounts don't match.\n\nFix this by only clearing RTF_ADDRCONF when the existing route does\nnot have a gateway. Routes without a gateway cannot qualify for ECMP\nanyway (rt6_qualify_for_ecmp() requires fib_nh_gw_family), so clearing\nRTF_ADDRCONF on them is safe and matches the original intent of the\ncommit.\n\n[0]:\nkernel BUG at net/ipv6/ip6_fib.c:1217!\nOops: invalid opcode: 0000 [#1] SMP KASAN PTI\nCPU: 0 UID: 0 PID: 6010 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)\nHardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025\nRIP: 0010:fib6_add_rt2node+0x3433/0x3470 net/ipv6/ip6_fib.c:1217\n[...]\nCall Trace:\n <TASK>\n fib6_add+0x8da/0x18a0 net/ipv6/ip6_fib.c:1532\n __ip6_ins_rt net/ipv6/route.c:1351 [inline]\n ip6_route_add+0xde/0x1b0 net/ipv6/route.c:3946\n ipv6_route_ioctl+0x35c/0x480 net/ipv6/route.c:4571\n inet6_ioctl+0x219/0x280 net/ipv6/af_inet6.c:577\n sock_do_ioctl+0xdc/0x300 net/socket.c:1245\n sock_ioctl+0x576/0x790 net/socket.c:1366\n vfs_ioctl fs/ioctl.c:51 [inline]\n __do_sys_ioctl fs/ioctl.c:597 [inline]\n __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583\n do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]\n do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94\n entry_SYSCALL_64_after_hwframe+0x77/0x7f\n\n## Affected\n\n- `Linux >= cb2b0caa8ca93cbe39177516669bf699c74f7041 < 50b7c7a255858a85c4636a1e990ca04591153dca`\n- `Linux >= 03f642caab84bbfd138e74f671bb436186ea7e82 < d8143c54ceeba232dc8a13aa0afa14a44b371d93`\n- `Linux >= 3e5b25da0b4109a3e063759735e6ec4236ea5a05 < b8ad2d53f706aeea833d23d45c0758398fede580`\n- `Linux >= f72514b3c5698e4b900b25345e09f9ed33123de6 < bbf4a17ad9ffc4e3d7ec13d73ecd59dea149ed25`\n- `Linux 61d88ea0f30c88e4ea98793594943aed8f1fc9ab`\n- `Linux >= 6.17.13 < 6.18`\n- `Linux >= 6.6.120 < 6.6.124`\n- `Linux >= 6.12.63 < 6.12.70`\n- `Linux >= 6.18.2 < 6.18.10`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}