In the Linux kernel, the following vulnerability has been resolved:
vxlan: mdb: Fix use-after-free in vxlan_mdb_remote_src_del()
vxlan_mdb_is_valid_source(), which validates MDBE_ATTR_SOURCE and every
MDBE_ATTR_SRC_LIST member, accepts the all-zeros address.
A source list is only accepted on a (*, G) entry, whose source is the
all-zeros address, and for each member of the list an (S, G) entry is
derived from it by substituting the source. Entries are keyed by a plain
memcmp() of struct vxlan_mdb_entry_key, so if MDBE_ATTR_SOURCE is present
and holds the all-zeros address and the source list holds it as well, the
derived (S, G) key is byte-identical to the (*, G) key and resolves to the
same entry. Omitting MDBE_ATTR_SOURCE is not equivalent, as the key is
then left with a zero address family.
vxlan_mdb_remote_src_del() removes the forwarding entry of a source before
freeing the source entry:
vxlan_mdb_remote_src_fwd_del(vxlan, group, remote, &ent->addr);
vxlan_mdb_remote_src_entry_del(ent);
With the keys aliased, the first call deletes the remote of the entry that
owns 'ent' instead of a separate (S, G) entry, and frees 'ent'. The second
call then runs on the freed entry, and its hlist_del() reads ->pprev and
->next out of it and writes through them.
Adding the (*, G) entry with NLM_F_REPLACE and no source list marks the
all-zeros source for deletion and reaches this from the sweep at the end
of vxlan_mdb_remote_srcs_replace().
BUG: KASAN: slab-use-after-free in __vxlan_mdb_add+0x1cd/0xd70
Read of size 8 at addr ffff888102852500 by task poc/84
__vxlan_mdb_add+0x1cd/0xd70
vxlan_mdb_add+0xc0/0x140
rtnl_mdb_add+0x157/0x2a0
rtnetlink_rcv_msg+0x207/0x5a0
Allocated by task 84:
__kmalloc_cache_noprof+0x153/0x360
vxlan_mdb_remote_srcs_add+0x2eb/0x440
__vxlan_mdb_add+0x803/0xd70
Freed by task 84:
kfree+0x14c/0x3b0
vxlan_mdb_remote_del+0x129/0x1a0
__vxlan_mdb_del+0x4f/0xe0
vxlan_mdb_remote_src_fwd_del.isra.0+0x162/0x1b0
__vxlan_mdb_add+0x1c5/0xd70
The MDB operations are netns-scoped, so an unprivileged user can perform
them in a new user and network namespace.
Reject the all-zeros address in vxlan_mdb_is_valid_source(), which covers
both call sites. A (*, G) entry is expressed by omitting the source, so
nothing legitimate is refused.
Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>
vxlan: mdb: Fix use-after-free in vxlan_mdb_remote_src_del()
vxlan_mdb_is_valid_source(), which validates MDBE_ATTR_SOURCE and every
MDBE_ATTR_SRC_LIST member, accepts the all-zeros address.
A source list is only accepted on a (*, G) entry, whose source is the
all-zeros address, and for each member of the list an (S, G) entry is
derived from it by substituting the source. Entries are keyed by a plain
memcmp() of struct vxlan_mdb_entry_key, so if MDBE_ATTR_SOURCE is present
and holds the all-zeros address and the source list holds it as well, the
derived (S, G) key is byte-identical to the (*, G) key and resolves to the
same entry. Omitting MDBE_ATTR_SOURCE is not equivalent, as the key is
then left with a zero address family.
vxlan_mdb_remote_src_del() removes the forwarding entry of a source before
freeing the source entry:
vxlan_mdb_remote_src_fwd_del(vxlan, group, remote, &ent->addr);
vxlan_mdb_remote_src_entry_del(ent);
With the keys aliased, the first call deletes the remote of the entry that
owns 'ent' instead of a separate (S, G) entry, and frees 'ent'. The second
call then runs on the freed entry, and its hlist_del() reads ->pprev and
->next out of it and writes through them.
Adding the (*, G) entry with NLM_F_REPLACE and no source list marks the
all-zeros source for deletion and reaches this from the sweep at the end
of vxlan_mdb_remote_srcs_replace().
BUG: KASAN: slab-use-after-free in __vxlan_mdb_add+0x1cd/0xd70
Read of size 8 at addr ffff888102852500 by task poc/84
__vxlan_mdb_add+0x1cd/0xd70
vxlan_mdb_add+0xc0/0x140
rtnl_mdb_add+0x157/0x2a0
rtnetlink_rcv_msg+0x207/0x5a0
Allocated by task 84:
__kmalloc_cache_noprof+0x153/0x360
vxlan_mdb_remote_srcs_add+0x2eb/0x440
__vxlan_mdb_add+0x803/0xd70
Freed by task 84:
kfree+0x14c/0x3b0
vxlan_mdb_remote_del+0x129/0x1a0
__vxlan_mdb_del+0x4f/0xe0
vxlan_mdb_remote_src_fwd_del.isra.0+0x162/0x1b0
__vxlan_mdb_add+0x1c5/0xd70
The MDB operations are netns-scoped, so an unprivileged user can perform
them in a new user and network namespace.
Reject the all-zeros address in vxlan_mdb_is_valid_source(), which covers
both call sites. A (*, G) entry is expressed by omitting the source, so
nothing legitimate is refused.
Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
|||||||||||||||||||||
| Linux | Linux | affected |
|
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Advisories
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Fixes
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
References
History
Fri, 25 Sep 2026 10:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: vxlan: mdb: Fix use-after-free in vxlan_mdb_remote_src_del() vxlan_mdb_is_valid_source(), which validates MDBE_ATTR_SOURCE and every MDBE_ATTR_SRC_LIST member, accepts the all-zeros address. A source list is only accepted on a (*, G) entry, whose source is the all-zeros address, and for each member of the list an (S, G) entry is derived from it by substituting the source. Entries are keyed by a plain memcmp() of struct vxlan_mdb_entry_key, so if MDBE_ATTR_SOURCE is present and holds the all-zeros address and the source list holds it as well, the derived (S, G) key is byte-identical to the (*, G) key and resolves to the same entry. Omitting MDBE_ATTR_SOURCE is not equivalent, as the key is then left with a zero address family. vxlan_mdb_remote_src_del() removes the forwarding entry of a source before freeing the source entry: vxlan_mdb_remote_src_fwd_del(vxlan, group, remote, &ent->addr); vxlan_mdb_remote_src_entry_del(ent); With the keys aliased, the first call deletes the remote of the entry that owns 'ent' instead of a separate (S, G) entry, and frees 'ent'. The second call then runs on the freed entry, and its hlist_del() reads ->pprev and ->next out of it and writes through them. Adding the (*, G) entry with NLM_F_REPLACE and no source list marks the all-zeros source for deletion and reaches this from the sweep at the end of vxlan_mdb_remote_srcs_replace(). BUG: KASAN: slab-use-after-free in __vxlan_mdb_add+0x1cd/0xd70 Read of size 8 at addr ffff888102852500 by task poc/84 __vxlan_mdb_add+0x1cd/0xd70 vxlan_mdb_add+0xc0/0x140 rtnl_mdb_add+0x157/0x2a0 rtnetlink_rcv_msg+0x207/0x5a0 Allocated by task 84: __kmalloc_cache_noprof+0x153/0x360 vxlan_mdb_remote_srcs_add+0x2eb/0x440 __vxlan_mdb_add+0x803/0xd70 Freed by task 84: kfree+0x14c/0x3b0 vxlan_mdb_remote_del+0x129/0x1a0 __vxlan_mdb_del+0x4f/0xe0 vxlan_mdb_remote_src_fwd_del.isra.0+0x162/0x1b0 __vxlan_mdb_add+0x1c5/0xd70 The MDB operations are netns-scoped, so an unprivileged user can perform them in a new user and network namespace. Reject the all-zeros address in vxlan_mdb_is_valid_source(), which covers both call sites. A (*, G) entry is expressed by omitting the source, so nothing legitimate is refused. Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com> | |
| Title | vxlan: mdb: Fix use-after-free in vxlan_mdb_remote_src_del() | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-09-25T10:36:05.369Z
Reserved: 2026-09-25T10:25:14.318Z
Link: CVE-2026-98122
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-09-25T11:17:43.470
Modified: 2026-09-25T11:17:43.470
Link: CVE-2026-98122
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.