{"id":"CVE-2026-98487","state":"PUBLISHED","title":"net: bridge: mdb: restart port group walk after deletion","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: bridge: mdb: restart port group walk after deletion\n\nbr_mdb_flush_pgs() keeps a pointer-to-pointer cursor while walking\nmp->ports. br_multicast_del_pg() can re-enter the same MDB entry through\nbr_multicast_sg_del_exclude_ports() and unlink other port groups. If the\ncursor points into one of those groups, the next iteration dereferences a\nstale cursor and can leave mp->ports pointing at freed memory.\n\nA following RTM_GETMDB exposes the dangling pointer:\n\n  BUG: KASAN: slab-use-after-free in br_mdb_dump\n  Read of size 8\n    br_mdb_dump\n    rtnl_mdb_dump\n    rtnl_dumpit\n    netlink_dump\n\nReset the cursor to mp->ports after every deletion. The deletion removes at\nleast the selected group, so the restarted walk always makes progress.","publishedAt":"2026-10-18T15:16:04.746Z","updatedAt":"2026-10-24T14:09:03.998Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"a6acb535afb2a3b688a7858f05b61f0433e480d5","status":"affected","lessThan":"46ec55855c972504258c371677ac039ba20e5d12","versionType":"git"},{"version":"a6acb535afb2a3b688a7858f05b61f0433e480d5","status":"affected","lessThan":"ab3c4a4c85f2e1e8d04b5c1770dea8412d21c7fe","versionType":"git"},{"version":"a6acb535afb2a3b688a7858f05b61f0433e480d5","status":"affected","lessThan":"fe2a42789c12eb7c5d3a42191e2cc735a6c35ead","versionType":"git"},{"version":"a6acb535afb2a3b688a7858f05b61f0433e480d5","status":"affected","lessThan":"ab1404ac81154a89fb61ac50ae9a04cd8d4834dc","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/bridge/br_mdb.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.8","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.8","versionType":"semver"},{"version":"6.12.112","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.55","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.9","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/bridge/br_mdb.c"]}],"references":["https://git.kernel.org/stable/c/46ec55855c972504258c371677ac039ba20e5d12","https://git.kernel.org/stable/c/ab3c4a4c85f2e1e8d04b5c1770dea8412d21c7fe","https://git.kernel.org/stable/c/fe2a42789c12eb7c5d3a42191e2cc735a6c35ead","https://git.kernel.org/stable/c/ab1404ac81154a89fb61ac50ae9a04cd8d4834dc"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:43.249Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/98xxx/CVE-2026-98487.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-98487","state":"PUBLISHED","datePublished":"2026-10-18T15:16:04.746Z","dateUpdated":"2026-10-24T14:09:03.998Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:25:14.352Z"},"containers":{"cna":{"title":"net: bridge: mdb: restart port group walk after deletion","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: bridge: mdb: restart port group walk after deletion\n\nbr_mdb_flush_pgs() keeps a pointer-to-pointer cursor while walking\nmp->ports. br_multicast_del_pg() can re-enter the same MDB entry through\nbr_multicast_sg_del_exclude_ports() and unlink other port groups. If the\ncursor points into one of those groups, the next iteration dereferences a\nstale cursor and can leave mp->ports pointing at freed memory.\n\nA following RTM_GETMDB exposes the dangling pointer:\n\n  BUG: KASAN: slab-use-after-free in br_mdb_dump\n  Read of size 8\n    br_mdb_dump\n    rtnl_mdb_dump\n    rtnl_dumpit\n    netlink_dump\n\nReset the cursor to mp->ports after every deletion. The deletion removes at\nleast the selected group, so the restarted walk always makes progress."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"a6acb535afb2a3b688a7858f05b61f0433e480d5","status":"affected","lessThan":"46ec55855c972504258c371677ac039ba20e5d12","versionType":"git"},{"version":"a6acb535afb2a3b688a7858f05b61f0433e480d5","status":"affected","lessThan":"ab3c4a4c85f2e1e8d04b5c1770dea8412d21c7fe","versionType":"git"},{"version":"a6acb535afb2a3b688a7858f05b61f0433e480d5","status":"affected","lessThan":"fe2a42789c12eb7c5d3a42191e2cc735a6c35ead","versionType":"git"},{"version":"a6acb535afb2a3b688a7858f05b61f0433e480d5","status":"affected","lessThan":"ab1404ac81154a89fb61ac50ae9a04cd8d4834dc","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/bridge/br_mdb.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.8","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.8","versionType":"semver"},{"version":"6.12.112","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.55","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.9","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/bridge/br_mdb.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/46ec55855c972504258c371677ac039ba20e5d12"},{"url":"https://git.kernel.org/stable/c/ab3c4a4c85f2e1e8d04b5c1770dea8412d21c7fe"},{"url":"https://git.kernel.org/stable/c/fe2a42789c12eb7c5d3a42191e2cc735a6c35ead"},{"url":"https://git.kernel.org/stable/c/ab1404ac81154a89fb61ac50ae9a04cd8d4834dc"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - A local sendmsg() on NETLINK_ROUTE carrying RTM_DELMDB with NLM_F_BULK reaches the patched br_mdb_flush_pgs() through rtnl_mdb_del() and ndo_mdb_del_bulk; received bridge packets do not enter this bulk-delete path.\nAC:L - The attacker can add a *,G EXCLUDE membership and permanent static S,G groups so br_multicast_sg_add_exclude_ports() creates skipped kernel-protocol STAR_EXCL nodes; a proto-static bulk flush then deterministically invalidates pp without a race.\nPR:L - rtnetlink_rcv_msg() requires CAP_NET_ADMIN through netlink_net_capable(), but an unprivileged user can obtain that capability in a user-created network namespace and create the bridge, ports, and MDB state there.\nUI:N - The attacker performs the RTM_NEWMDB setup, NLM_F_BULK RTM_DELMDB trigger, and optional RTM_GETMDB traversal through their own netlink socket; no victim action is required.\nS:U - The dangling mp->ports pointer corrupts and exposes bridge objects within the host kernel's existing security authority; it does not cross a guest-host, hypervisor, or IOMMU boundary.\nC:H - The persistent slab UAF lets reclaimed contents control p->next and p->key.port; br_mdb_fill_info() follows these links and returns port, timer, flag, and source-list data through RTM_GETMDB, enabling kernel-memory disclosure.\nI:H - Reusing the dangling node in br_multicast_del_pg() reaches hlist_del_init_rcu() through reclaimed pg->mglist.pprev and updates rhashtable and GC links, providing attacker-influenced kernel writes and potential control-flow hijacking.\nA:H - After br_multicast_destroy_port_group() calls kfree_rcu(), br_mdb_dump() produces the confirmed slab-use-after-free; stale p->key.port or p->next dereferences in dump or br_multicast_flood can oops or panic the kernel."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-24T14:09:03.998Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.8","versionEndExcluding":"6.12.112"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.8","versionEndExcluding":"6.18.55"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.8","versionEndExcluding":"7.2.9"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.8","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}