CVE intelligence and bounded remediation

CVE-2025-21977 — Linux Linux Kernel security vulnerability

Medium CVSS 5.5

In the Linux kernel, the following vulnerability has been resolved: fbdev: hyperv_fb: Fix hang in kdump kernel when on Hyper-V Gen 2 VMs Gen 2 Hyper-V VMs boot via EFI and have a standard EFI framebuffer device. When the kdump kernel runs in such a VM, loading the efifb driver may hang because of accessing the framebuffer at the wrong memory address. The scenario occurs when the hyperv_fb driver in the original kernel moves the framebuffer to a different MMIO address because of conflicts with an already-running efifb or simplefb driver. The hyperv_fb driver then informs Hyper-V of the change, which is allowed by the Hyper-V FB VMBus device protocol. However, when the kexec command loads the kdump kernel into crash memory via the kexec_file_load() system call, the system call doesn't know the framebuffer has moved, and it sets up the kdump screen_info using the original framebuffer address. The transition to the kdump kernel does not go through the Hyper-V host, so Hyper-V does not reset the framebuffer address like it would do on a reboot. When efifb tries to run, it accesses a non-existent framebuffer address, which traps to the Hyper-V host. After many such accesses, the Hyper-V…

Severity
Medium
CVSS
5.5 (3.1)
Published
2025-04-01
CISA KEV
Not currently listed
Ecosystem
linux/kernel

Affected products

  • linux / linux_kernel
  • linux / linux_kernel / 6.14

Showing 2 representative product identities from 8 source matches. Confirm exact affected versions with the linked vendor and NVD evidence.

Matched remediation archetype

General vulnerability remediation

This catalog composition supplies bounded fallback guidance. Explicitly reviewed curated workflows load with the complete record below.

Check exposure

  • Confirm the affected component, deployment paths, reachable interfaces, and enabled features from inventories and configuration, without probing production destructively.
  • Compare the advisory's affected conditions with the repository lockfiles, build manifests, artifacts, and runtime inventory.
  • Identify data sensitivity, trust boundaries, and privilege level for every confirmed affected deployment.

Remediate safely

  • Apply a vendor-supported fix or remove the affected component or feature; record the selected change and its source in the repository.
  • Update direct and transitive dependency locks, generated artifacts, deployment manifests, and asset inventories together.
  • Add a regression test for the documented unsafe condition using inert inputs and preserve rollback instructions.

Authoritative sources

Complete CVE record and remediation plan

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