# CVE-2026-31517: xfrm: iptfs: fix skb_put() panic on non-linear skb during reassembly

> A remote attacker can cause a kernel panic and system crash by sending crafted IP-TFS fragments that trigger a linearization assertion failure.

- **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 Apr 2026
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2026-31517, DEBIAN-CVE-2026-31517, GHSA-759f-2cpp-x5g6, UBUNTU-CVE-2026-31517

## What is CVE-2026-31517?

CVE-2026-31517 is a medium-severity denial of service vulnerability in Linux kernel, published on 22 Apr 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:

xfrm: iptfs: fix skb_put() panic on non-linear skb during reassembly

In iptfs_reassem_cont(), IP-TFS attempts to append data to the new inner
packet 'newskb' that is being reassembled. First a zero-copy approach is
tried if it succeeds then newskb becomes non-linear.

When a subsequent fragment in the same datagram does not meet the
fast-path conditions, a memory copy is performed. It calls skb_put() to
append the data and as newskb is non-linear it triggers
SKB_LINEAR_ASSERT check.

 Oops: invalid opcode: 0000 [#1] SMP NOPTI
 [...]
 RIP: 0010:skb_put+0x3c/0x40
 [...]
 Call Trace:
  <IRQ>
  iptfs_reassem_cont+0x1ab/0x5e0 [xfrm_iptfs]
  iptfs_input_ordered+0x2af/0x380 [xfrm_iptfs]
  iptfs_input+0x122/0x3e0 [xfrm_iptfs]
  xfrm_input+0x91e/0x1a50
  xfrm4_esp_rcv+0x3a/0x110
  ip_protocol_deliver_rcu+0x1d7/0x1f0
  ip_local_deliver_finish+0xbe/0x1e0
  __netif_receive_skb_core.constprop.0+0xb56/0x1120
  __netif_receive_skb_list_core+0x133/0x2b0
  netif_receive_skb_list_internal+0x1ff/0x3f0
  napi_complete_done+0x81/0x220
  virtnet_poll+0x9d6/0x116e [virtio_net]
  __napi_poll.constprop.0+0x2b/0x270
  net_rx_action+0x162/0x360
  handle_softirqs+0xdc/0x510
  __irq_exit_rcu+0xe7/0x110
  irq_exit_rcu+0xe/0x20
  common_interrupt+0x85/0xa0
  </IRQ>
  <TASK>

Fix this by checking if the skb is non-linear. If it is, linearize it by
calling skb_linearize(). As the initial allocation of newskb originally
reserved enough tailroom for the entire reassembled packet we do not
need to check if we have enough tailroom or extend it.

Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime)

## Which versions are affected by CVE-2026-31517?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31517?

Apply the vendor's patch.

## Is CVE-2026-31517 being exploited?

There is no known exploitation of CVE-2026-31517 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-2026-31517 and fix it if it is affected.

What it is: CVE-2026-31517 is a medium-severity denial of service vulnerability in Linux kernel, published on 22 Apr 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-2026-31517 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-2026-31517/ (Markdown: https://insights.sbomify.com/CVE-2026-31517/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31517
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31517
- OSV: https://osv.dev/vulnerability/CVE-2026-31517

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31517/
Summaries are generated and may contain mistakes; the official description above is the record.