# CVE-2026-31517: CVE-2026-31517

Status: published. Published: 2026-04-22. Updated: 2026-11-11.

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.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67) — https://git.kernel.org/stable/c/0b352f83cabfefdaafa806d6471f0eca117dc7d5
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67) — https://git.kernel.org/stable/c/33a7b36268933c75bdc355e5531951e0ea9f1951
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67) — https://git.kernel.org/stable/c/7fdfe8f6efeb0e1200e22a903f2471539f54522b

## Affected products and versions

- linux / linux_kernel: ≥ 6.14.1; < 6.18.21 (affected, custom). Source: NVD
- linux / linux_kernel: ≥ 6.19; < 6.19.11 (affected, custom). Source: NVD
- linux / linux_kernel: 6.14 (affected, custom). Source: NVD
- linux / linux_kernel: 7.0 (affected, custom). Source: NVD

## NVD configuration conditions

Affected CPE matches depend on the following AND/OR and negation conditions:

```json
[
  {
    "negate": false,
    "nodes": [
      {
        "cpeMatch": [
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
            "versionEndExcluding": "6.18.21",
            "versionStartIncluding": "6.14.1",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
            "versionEndExcluding": "6.19.11",
            "versionStartIncluding": "6.19",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:6.14:-:*:*:*:*:*:*",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc6:*:*:*:*:*:*",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc7:*:*:*:*:*:*",
            "vulnerable": true
          }
        ],
        "negate": false,
        "operator": "OR"
      }
    ],
    "operator": "OR"
  }
]
```

## Severity and prioritization

- CVSS 3.1: 5.5 (medium); CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H; source: NVD: nvd@nist.gov

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-401

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/0b352f83cabfefdaafa806d6471f0eca117dc7d5 (416baaa9-dc9f-4396-8d5f-8c081fb06d67; Patch)

- https://git.kernel.org/stable/c/33a7b36268933c75bdc355e5531951e0ea9f1951 (416baaa9-dc9f-4396-8d5f-8c081fb06d67; Patch)

- https://git.kernel.org/stable/c/7fdfe8f6efeb0e1200e22a903f2471539f54522b (416baaa9-dc9f-4396-8d5f-8c081fb06d67; Patch)

## Provenance

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31517; retrieved 2026-11-12; source updated 2026-11-11

Revision: fc8f355b63c7f557722ac018e9e61387ab3a4defc190f4771bf2a2d7724659fd

Canonical: https://y2.dev/cve/CVE-2026-31517

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