# CVE-2025-40102: KVM: arm64: Prevent access to vCPU events before init

> A local attacker can trigger a kernel crash in KVM arm64 by accessing uninitialized vCPU events, causing a denial of service.

- **Severity:** Not scored
- **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:** 30 Oct 2025
- **Updated:** 2 Sep 2026
- **Also known as:** AZL-69412, BELL-CVE-2025-40102, DEBIAN-CVE-2025-40102, GHSA-82mj-rf9f-84h3, ROOT-OS-DEBIAN-11-CVE-2025-40102, ROOT-OS-DEBIAN-12-CVE-2025-40102, ROOT-OS-DEBIAN-13-CVE-2025-40102, ROOT-OS-UBUNTU-2204-CVE-2025-40102, ROOT-OS-UBUNTU-2404-CVE-2025-40102, UBUNTU-CVE-2025-40102

## What is CVE-2025-40102?

CVE-2025-40102 is a vulnerability in Linux, published on 30 Oct 2025. 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:

KVM: arm64: Prevent access to vCPU events before init

Another day, another syzkaller bug. KVM erroneously allows userspace to
pend vCPU events for a vCPU that hasn't been initialized yet, leading to
KVM interpreting a bunch of uninitialized garbage for routing /
injecting the exception.

In one case the injection code and the hyp disagree on whether the vCPU
has a 32bit EL1 and put the vCPU into an illegal mode for AArch64,
tripping the BUG() in exception_target_el() during the next injection:

  kernel BUG at arch/arm64/kvm/inject_fault.c:40!
  Internal error: Oops - BUG: 00000000f2000800 [#1]  SMP
  CPU: 3 UID: 0 PID: 318 Comm: repro Not tainted 6.17.0-rc4-00104-g10fd0285305d #6 PREEMPT
  Hardware name: linux,dummy-virt (DT)
  pstate: 21402009 (nzCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
  pc : exception_target_el+0x88/0x8c
  lr : pend_serror_exception+0x18/0x13c
  sp : ffff800082f03a10
  x29: ffff800082f03a10 x28: ffff0000cb132280 x27: 0000000000000000
  x26: 0000000000000000 x25: ffff0000c2a99c20 x24: 0000000000000000
  x23: 0000000000008000 x22: 0000000000000002 x21: 0000000000000004
  x20: 0000000000008000 x19: ffff0000c2a99c20 x18: 0000000000000000
  x17: 0000000000000000 x16: 0000000000000000 x15: 00000000200000c0
  x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
  x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000
  x8 : ffff800082f03af8 x7 : 0000000000000000 x6 : 0000000000000000
  x5 : ffff800080f621f0 x4 : 0000000000000000 x3 : 0000000000000000
  x2 : 000000000040009b x1 : 0000000000000003 x0 : ffff0000c2a99c20
  Call trace:
   exception_target_el+0x88/0x8c (P)
   kvm_inject_serror_esr+0x40/0x3b4
   __kvm_arm_vcpu_set_events+0xf0/0x100
   kvm_arch_vcpu_ioctl+0x180/0x9d4
   kvm_vcpu_ioctl+0x60c/0x9f4
   __arm64_sys_ioctl+0xac/0x104
   invoke_syscall+0x48/0x110
   el0_svc_common.constprop.0+0x40/0xe0
   do_el0_svc+0x1c/0x28
   el0_svc+0x34/0xf0
   el0t_64_sync_handler+0xa0/0xe4
   el0t_64_sync+0x198/0x19c
  Code: f946bc01 b4fffe61 9101e020 17fffff2 (d4210000)

Reject the ioctls outright as no sane VMM would call these before
KVM_ARM_VCPU_INIT anyway. Even if it did the exception would've been
thrown away by the eventual reset of the vCPU's state.

## Which versions are affected by CVE-2025-40102?


## How do I fix CVE-2025-40102?

Apply the vendor's patch.

## Is CVE-2025-40102 being exploited?

There is no known exploitation of CVE-2025-40102 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40102 and fix it if it is affected.

What it is: CVE-2025-40102 is a vulnerability in Linux, published on 30 Oct 2025. 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-2025-40102 in the wild and no public exploit code.

Affected product: Linux. 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-2025-40102/ (Markdown: https://insights.sbomify.com/CVE-2025-40102/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40102
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40102
- OSV: https://osv.dev/vulnerability/CVE-2025-40102

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40102/
Summaries are generated and may contain mistakes; the official description above is the record.