---
cve: "CVE-2026-31504"
severity: "HIGH"
cvss: 7.8
epss: "14%"
vendor: "Linux"
kev: false
exploited: false
published: "2026-04-22 14:16:49"
tags: [cve, security, high]
source: tsecurity.de CVE-Dossier
exported: "2026-09-16T09:49:43+02:00"
---

# CVE-2026-31504

> 7.8 HIGH

## Beschreibung

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

net: fix fanout UAF in packet_release() via NETDEV_UP race

`packet_release()` has a race window where `NETDEV_UP` can re-register a
socket into a fanout group's `arr[]` array. The re-registration is not
cleaned up by `fanout_release()`, leaving a dangling pointer in the fanout
array.
`packet_release()` does NOT zero `po->num` in its `bind_lock` section.
After releasing `bind_lock`, `po->num` is still non-zero and `po->ifindex`
still matches the bound device. A concurrent `packet_notifier(NETDEV_UP)`
that already found the socket in `sklist` can re-register the hook.
For fanout sockets, this re-registration calls `__fanout_link(sk, po)`
which adds the socket back into `f->arr[]` and increments `f->num_members`,
but does NOT increment `f->sk_ref`.

The fix sets `po->num` to zero in `packet_release` while `bind_lock` is
held to prevent NETDEV_UP from linking, preventing the race window.

This bug was found following an additional audit with Claude Code based
on CVE-2025-38617.

## CVSS-Vektor

```
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Lokal | good |
| AC Komplexität | Gering | bad |
| PR Privilegien | Gering | warn |
| UI Interaktion | Keine | bad |
| S Scope | Unverändert | good |
| C Vertraulichkeit | Hoch | bad |
| I Integrität | Hoch | bad |
| A Verfügbarkeit | Hoch | bad |

## Patch verfügbar (OSV)

- Kernel ≥ 5.10.253
- Kernel ≥ 5.15.203
- Kernel ≥ 6.1.168
- Kernel ≥ 6.6.131
- Kernel ≥ 6.12.80
- Kernel ≥ 6.18.21
- Kernel ≥ 6.19.11

## Referenzen

- <https://git.kernel.org/stable/c/ee642b1962caa9aa231c01abbd58bc453ae6b66e>
- <https://git.kernel.org/stable/c/42cfd7898eeed290c9fb73f732af1f7d6b0a703e>
- <https://git.kernel.org/stable/c/1b4c03f8892d955385c202009af7485364731bb9>
- <https://git.kernel.org/stable/c/654386baef228c2992dbf604c819e4c7c35fc71b>
- <https://git.kernel.org/stable/c/75fe6db23705a1d55160081f7b37db9665b1880b>
- <https://git.kernel.org/stable/c/d0c7cdc15fdf8c4f91aca1928e52295d175b6ec6>
- <https://git.kernel.org/stable/c/ceccbfc6de720ad633519a226715989cfb065af1>
- <https://git.kernel.org/stable/c/42156f93d123436f2a27c468f18c966b7e5db796>
- <https://cert-portal.siemens.com/productcert/html/ssa-019113.html>
- <https://cert-portal.siemens.com/productcert/html/ssa-082556.html>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-31504) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_