# CVE-2025-21855: ibmvnic: Don't reference skb after sending to VIOS

> A use-after-free vulnerability in the Linux kernel ibmvnic driver allows attackers to cause a denial of service or potentially execute code via race conditions during packet transmission.

- **Severity:** High 8.6 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 12 Mar 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-21855, DEBIAN-CVE-2025-21855, GHSA-5jpx-997x-jhrp, ROOT-OS-DEBIAN-11-CVE-2025-21855, ROOT-OS-UBUNTU-2204-CVE-2025-21855, ROOT-OS-UBUNTU-2404-CVE-2025-21855, UBUNTU-CVE-2025-21855

## What is CVE-2025-21855?

CVE-2025-21855 is a high-severity use after free vulnerability in Linux kernel, published on 12 Mar 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

ibmvnic: Don't reference skb after sending to VIOS

Previously, after successfully flushing the xmit buffer to VIOS,
the tx_bytes stat was incremented by the length of the skb.

It is invalid to access the skb memory after sending the buffer to
the VIOS because, at any point after sending, the VIOS can trigger
an interrupt to free this memory. A race between reading skb->len
and freeing the skb is possible (especially during LPM) and will
result in use-after-free:
 ==================================================================
 BUG: KASAN: slab-use-after-free in ibmvnic_xmit+0x75c/0x1808 [ibmvnic]
 Read of size 4 at addr c00000024eb48a70 by task hxecom/14495
 <...>
 Call Trace:
 [c000000118f66cf0] [c0000000018cba6c] dump_stack_lvl+0x84/0xe8 (unreliable)
 [c000000118f66d20] [c0000000006f0080] print_report+0x1a8/0x7f0
 [c000000118f66df0] [c0000000006f08f0] kasan_report+0x128/0x1f8
 [c000000118f66f00] [c0000000006f2868] __asan_load4+0xac/0xe0
 [c000000118f66f20] [c0080000046eac84] ibmvnic_xmit+0x75c/0x1808 [ibmvnic]
 [c000000118f67340] [c0000000014be168] dev_hard_start_xmit+0x150/0x358
 <...>
 Freed by task 0:
 kasan_save_stack+0x34/0x68
 kasan_save_track+0x2c/0x50
 kasan_save_free_info+0x64/0x108
 __kasan_mempool_poison_object+0x148/0x2d4
 napi_skb_cache_put+0x5c/0x194
 net_tx_action+0x154/0x5b8
 handle_softirqs+0x20c/0x60c
 do_softirq_own_stack+0x6c/0x88
 <...>
 The buggy address belongs to the object at c00000024eb48a00 which
  belongs to the cache skbuff_head_cache of size 224
==================================================================

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2025-21855?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21855?

Apply the vendor's patch.

## Is CVE-2025-21855 being exploited?

There is no known exploitation of CVE-2025-21855 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-2025-21855 and fix it if it is affected.

What it is: CVE-2025-21855 is a high-severity use after free vulnerability in Linux kernel, published on 12 Mar 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-21855 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-2025-21855/ (Markdown: https://insights.sbomify.com/CVE-2025-21855/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21855
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21855
- OSV: https://osv.dev/vulnerability/CVE-2025-21855

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21855/
Summaries are generated and may contain mistakes; the official description above is the record.