---
cve: "CVE-2025-40123"
severity: "HIGH"
cvss: 7.8
epss: "16%"
vendor: "Linux"
kev: false
exploited: false
published: "2025-11-12 11:15:41"
tags: [cve, security, high]
source: tsecurity.de CVE-Dossier
exported: "2026-09-19T08:43:31+02:00"
---

# CVE-2025-40123

> 7.8 HIGH

## Beschreibung

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

bpf: Enforce expected_attach_type for tailcall compatibility

Yinhao et al. recently reported:

  Our fuzzer tool discovered an uninitialized pointer issue in the
  bpf_prog_test_run_xdp() function within the Linux kernel's BPF subsystem.
  This leads to a NULL pointer dereference when a BPF program attempts to
  deference the txq member of struct xdp_buff object.

The test initializes two programs of BPF_PROG_TYPE_XDP: progA acts as the
entry point for bpf_prog_test_run_xdp() and its expected_attach_type can
neither be of be BPF_XDP_DEVMAP nor BPF_XDP_CPUMAP. progA calls into a slot
of a tailcall map it owns. progB's expected_attach_type must be BPF_XDP_DEVMAP
to pass xdp_is_valid_access() validation. The program returns struct xdp_md's
egress_ifindex, and the latter is only allowed to be accessed under mentioned
expected_attach_type. progB is then inserted into the tailcall which progA
calls.

The underlying issue goes beyond XDP though. Another example are programs
of type BPF_PROG_TYPE_CGROUP_SOCK_ADDR. sock_addr_is_valid_access() as well
as sock_addr_func_proto() have different logic depending on the programs'
expected_attach_type. Similarly, a program attached to BPF_CGROUP_INET4_GETPEERNAME
should not be allowed doing a tailcall into a program which calls bpf_bind()
out of BPF which is only enabled for BPF_CGROUP_INET4_CONNECT.

In short, specifying expected_attach_type allows to open up additional
functionality or restrictions beyond what the basic bpf_prog_type enables.
The use of tailcalls must not violate these constraints. Fix it by enforcing
expected_attach_type in __bpf_prog_map_compatible().

Note that we only enforce this for tailcall maps, but not for BPF devmaps or
cpumaps: There, the programs are invoked through dev_map_bpf_prog_run*() and
cpu_map_bpf_prog_run*() which set up a new environment / context and therefore
these situations are not prone to this issue.

## 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 ≥ 5.10.270
- Kernel ≥ 5.15.221
- Kernel ≥ 6.1.156
- Kernel ≥ 6.6.112
- Kernel ≥ 6.12.53
- Kernel ≥ 6.17.3

## Referenzen

- <https://git.kernel.org/stable/c/e53a59e7cee5c1605d1ed595933098c2b69108f9>
- <https://git.kernel.org/stable/c/dc4f348952173beb8ceb15be30b249276eccb605>
- <https://git.kernel.org/stable/c/a99de19128aec0913f3d529f529fbbff5edfaff8>
- <https://git.kernel.org/stable/c/08cb3dc9d2b44f153d0bcf2cb966e4a94b5d0f32>
- <https://git.kernel.org/stable/c/f856c598080ba7ce1252867b8ecd6ad5bdaf9a6a>
- <https://git.kernel.org/stable/c/c1ad19b5d8e23123503dcaf2d4342e1b90b923ad>
- <https://git.kernel.org/stable/c/4540aed51b12bc13364149bf95f6ecef013197c0>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2025-40123) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_