# CVE-2025-38638: ipv6: add a retry logic in net6_rt_notify()

> A race condition in Linux kernel IPv6 routing notifications can trigger a kernel warning and potential denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 22 Aug 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-38638, GHSA-4w7v-gw2g-gqwc, UBUNTU-CVE-2025-38638

## What is CVE-2025-38638?

CVE-2025-38638 is a medium-severity denial of service vulnerability in Linux kernel, published on 22 Aug 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:

ipv6: add a retry logic in net6_rt_notify()

inet6_rt_notify() can be called under RCU protection only.
This means the route could be changed concurrently
and rt6_fill_node() could return -EMSGSIZE.

Re-size the skb when this happens and retry, removing
one WARN_ON() that syzbot was able to trigger:

WARNING: CPU: 3 PID: 6291 at net/ipv6/route.c:6342 inet6_rt_notify+0x475/0x4b0 net/ipv6/route.c:6342
Modules linked in:
CPU: 3 UID: 0 PID: 6291 Comm: syz.0.77 Not tainted 6.16.0-rc7-syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
 RIP: 0010:inet6_rt_notify+0x475/0x4b0 net/ipv6/route.c:6342
Code: fc ff ff e8 6d 52 ea f7 e9 47 fc ff ff 48 8b 7c 24 08 4c 89 04 24 e8 5a 52 ea f7 4c 8b 04 24 e9 94 fd ff ff e8 9c fe 84 f7 90 <0f> 0b 90 e9 bd fd ff ff e8 6e 52 ea f7 e9 bb fb ff ff 48 89 df e8
RSP: 0018:ffffc900035cf1d8 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffffc900035cf540 RCX: ffffffff8a36e790
RDX: ffff88802f7e8000 RSI: ffffffff8a36e9d4 RDI: 0000000000000005
RBP: ffff88803c230f00 R08: 0000000000000005 R09: 00000000ffffffa6
R10: 00000000ffffffa6 R11: 0000000000000001 R12: 00000000ffffffa6
R13: 0000000000000900 R14: ffff888032ea4100 R15: 0000000000000000
FS:  00007fac7b89a6c0(0000) GS:ffff8880d6a20000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fac7b899f98 CR3: 0000000034b3f000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
  ip6_route_mpath_notify+0xde/0x280 net/ipv6/route.c:5356
  ip6_route_multipath_add+0x1181/0x1bd0 net/ipv6/route.c:5536
  inet6_rtm_newroute+0xe4/0x1a0 net/ipv6/route.c:5647
  rtnetlink_rcv_msg+0x95e/0xe90 net/core/rtnetlink.c:6944
  netlink_rcv_skb+0x155/0x420 net/netlink/af_netlink.c:2552
  netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
  netlink_unicast+0x58d/0x850 net/netlink/af_netlink.c:1346
  netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1896
  sock_sendmsg_nosec net/socket.c:712 [inline]
  __sock_sendmsg net/socket.c:727 [inline]
  ____sys_sendmsg+0xa95/0xc70 net/socket.c:2566
  ___sys_sendmsg+0x134/0x1d0 net/socket.c:2620

## Which versions are affected by CVE-2025-38638?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-38638?

Apply the vendor's patch.

## Is CVE-2025-38638 being exploited?

There is no known exploitation of CVE-2025-38638 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-2025-38638 and fix it if it is affected.

What it is: CVE-2025-38638 is a medium-severity denial of service vulnerability in Linux kernel, published on 22 Aug 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-2025-38638 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-2025-38638/ (Markdown: https://insights.sbomify.com/CVE-2025-38638/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38638
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38638
- OSV: https://osv.dev/vulnerability/CVE-2025-38638

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38638/
Summaries are generated and may contain mistakes; the official description above is the record.