# CVE-2025-37921: vxlan: vnifilter: Fix unlocked deletion of default FDB entry

> A race condition in the Linux kernel VXLAN driver allows local attackers to trigger a kernel warning and potential denial of service by deleting VNI filters without proper locking.

- **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:** 20 May 2025
- **Updated:** 15 Oct 2026
- **Also known as:** BELL-CVE-2025-37921, DEBIAN-CVE-2025-37921, GHSA-x58j-hw5g-jqcq, ROOT-OS-DEBIAN-12-CVE-2025-37921, ROOT-OS-UBUNTU-2404-CVE-2025-37921, UBUNTU-CVE-2025-37921

## What is CVE-2025-37921?

CVE-2025-37921 is a high-severity vulnerability in Debian Debian Linux, published on 20 May 2025. 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: vnifilter: Fix unlocked deletion of default FDB entry

When a VNI is deleted from a VXLAN device in 'vnifilter' mode, the FDB
entry associated with the default remote (assuming one was configured)
is deleted without holding the hash lock. This is wrong and will result
in a warning [1] being generated by the lockdep annotation that was
added by commit ebe642067455 ("vxlan: Create wrappers for FDB lookup").

Reproducer:

 # ip link add vx0 up type vxlan dstport 4789 external vnifilter local 192.0.2.1
 # bridge vni add vni 10010 remote 198.51.100.1 dev vx0
 # bridge vni del vni 10010 dev vx0

Fix by acquiring the hash lock before the deletion and releasing it
afterwards. Blame the original commit that introduced the issue rather
than the one that exposed it.

[1]
WARNING: CPU: 3 PID: 392 at drivers/net/vxlan/vxlan_core.c:417 vxlan_find_mac+0x17f/0x1a0
[...]
RIP: 0010:vxlan_find_mac+0x17f/0x1a0
[...]
Call Trace:
 <TASK>
 __vxlan_fdb_delete+0xbe/0x560
 vxlan_vni_delete_group+0x2ba/0x940
 vxlan_vni_del.isra.0+0x15f/0x580
 vxlan_process_vni_filter+0x38b/0x7b0
 vxlan_vnifilter_process+0x3bb/0x510
 rtnetlink_rcv_msg+0x2f7/0xb70
 netlink_rcv_skb+0x131/0x360
 netlink_unicast+0x426/0x710
 netlink_sendmsg+0x75a/0xc20
 __sock_sendmsg+0xc1/0x150
 ____sys_sendmsg+0x5aa/0x7b0
 ___sys_sendmsg+0xfc/0x180
 __sys_sendmsg+0x121/0x1b0
 do_syscall_64+0xbb/0x1d0
 entry_SYSCALL_64_after_hwframe+0x4b/0x53

## Which versions are affected by CVE-2025-37921?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-37921?

Apply the vendor's patch.

## Is CVE-2025-37921 being exploited?

There is no known exploitation of CVE-2025-37921 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-37921 and fix it if it is affected.

What it is: CVE-2025-37921 is a high-severity vulnerability in Debian Debian Linux, published on 20 May 2025. 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-2025-37921 in the wild and no public exploit code.

Affected product: Debian Debian Linux. 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-2025-37921/ (Markdown: https://insights.sbomify.com/CVE-2025-37921/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-37921
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-37921
- OSV: https://osv.dev/vulnerability/CVE-2025-37921

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-37921/
Summaries are generated and may contain mistakes; the official description above is the record.