{"id":"CVE-2026-98122","summary":"vxlan: mdb: Fix use-after-free in vxlan_mdb_remote_src_del()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nvxlan: mdb: Fix use-after-free in vxlan_mdb_remote_src_del()\n\nvxlan_mdb_is_valid_source(), which validates MDBE_ATTR_SOURCE and every\nMDBE_ATTR_SRC_LIST member, accepts the all-zeros address.\n\nA source list is only accepted on a (*, G) entry, whose source is the\nall-zeros address, and for each member of the list an (S, G) entry is\nderived from it by substituting the source. Entries are keyed by a plain\nmemcmp() of struct vxlan_mdb_entry_key, so if MDBE_ATTR_SOURCE is present\nand holds the all-zeros address and the source list holds it as well, the\nderived (S, G) key is byte-identical to the (*, G) key and resolves to the\nsame entry. Omitting MDBE_ATTR_SOURCE is not equivalent, as the key is\nthen left with a zero address family.\n\nvxlan_mdb_remote_src_del() removes the forwarding entry of a source before\nfreeing the source entry:\n\n\tvxlan_mdb_remote_src_fwd_del(vxlan, group, remote, &ent-\u003eaddr);\n\tvxlan_mdb_remote_src_entry_del(ent);\n\nWith the keys aliased, the first call deletes the remote of the entry that\nowns 'ent' instead of a separate (S, G) entry, and frees 'ent'. The second\ncall then runs on the freed entry, and its hlist_del() reads -\u003epprev and\n-\u003enext out of it and writes through them.\n\nAdding the (*, G) entry with NLM_F_REPLACE and no source list marks the\nall-zeros source for deletion and reaches this from the sweep at the end\nof vxlan_mdb_remote_srcs_replace().\n\n  BUG: KASAN: slab-use-after-free in __vxlan_mdb_add+0x1cd/0xd70\n  Read of size 8 at addr ffff888102852500 by task poc/84\n   __vxlan_mdb_add+0x1cd/0xd70\n   vxlan_mdb_add+0xc0/0x140\n   rtnl_mdb_add+0x157/0x2a0\n   rtnetlink_rcv_msg+0x207/0x5a0\n  Allocated by task 84:\n   __kmalloc_cache_noprof+0x153/0x360\n   vxlan_mdb_remote_srcs_add+0x2eb/0x440\n   __vxlan_mdb_add+0x803/0xd70\n  Freed by task 84:\n   kfree+0x14c/0x3b0\n   vxlan_mdb_remote_del+0x129/0x1a0\n   __vxlan_mdb_del+0x4f/0xe0\n   vxlan_mdb_remote_src_fwd_del.isra.0+0x162/0x1b0\n   __vxlan_mdb_add+0x1c5/0xd70\n\nThe MDB operations are netns-scoped, so an unprivileged user can perform\nthem in a new user and network namespace.\n\nReject the all-zeros address in vxlan_mdb_is_valid_source(), which covers\nboth call sites. A (*, G) entry is expressed by omitting the source, so\nnothing legitimate is refused.\n\nDiscovered by XBOW, triaged by Baul Lee \u003cbaul.lee@xbow.com\u003e","modified":"2026-09-26T03:48:33.338082294Z","published":"2026-09-25T10:36:05.369Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98122.json"},"references":[{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"},{"type":"WEB","url":"https://git.kernel.org/stable/c/4aa61c88b4e292e10abdfd791334b8272108d68a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/71203a41d6fa2fa0ea2f3a7541987958bd3694fd"},{"type":"WEB","url":"https://git.kernel.org/stable/c/74e2a56c82209b0335b53e25f19f9b0590e2483d"},{"type":"WEB","url":"https://git.kernel.org/stable/c/e12c903fd13c6261b98ca18d8f70ac26e739e2f8"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98122.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98122"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"a3a48de5eade770e911d35291217bdd69ce04ef1"},{"fixed":"e12c903fd13c6261b98ca18d8f70ac26e739e2f8"},{"fixed":"74e2a56c82209b0335b53e25f19f9b0590e2483d"},{"fixed":"71203a41d6fa2fa0ea2f3a7541987958bd3694fd"},{"fixed":"4aa61c88b4e292e10abdfd791334b8272108d68a"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98122.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.4.0"},{"fixed":"6.12.111"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.53"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.7"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98122.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}