# CVE-2026-98122: vxlan: mdb: Fix use-after-free in vxlan_mdb_remote_src_del()

> A use-after-free in the Linux kernel VXLAN module allows local attackers to execute arbitrary code or escalate privileges via crafted netlink messages.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** Yes
- **Published:** 25 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-104343, BELL-CVE-2026-98122, DEBIAN-CVE-2026-98122, GHSA-4jrj-q762-xjh5, UBUNTU-CVE-2026-98122

## What is CVE-2026-98122?

CVE-2026-98122 is a high-severity use after free vulnerability in Linux kernel, published on 25 Sep 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:

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>

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-98122?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-98122?

Apply the vendor's patch.

## Is CVE-2026-98122 being exploited?

There is no known exploitation of CVE-2026-98122 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98122 and fix it if it is affected.

What it is: CVE-2026-98122 is a high-severity use after free vulnerability in Linux kernel, published on 25 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-98122 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-98122/ (Markdown: https://insights.sbomify.com/CVE-2026-98122/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98122
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98122
- OSV: https://osv.dev/vulnerability/CVE-2026-98122

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98122/
Summaries are generated and may contain mistakes; the official description above is the record.