CVE-2025-21977

Kdump hang via stale framebuffer address

Published Apr 1, 2025 · Updated May 11, 2026

Denial of service in Linux hyperv_fb 6.8 allows local users to hang a Hyper-V Gen 2 guest during kdump via a stale framebuffer address. The driver removes conflicting framebuffers after MMIO allocation, allowing relocation while kexec_file_load records the original address in screen_info. Reaching the fault requires an EFI-booted Gen 2 guest, hyperv_fb relocation, and a crash kernel loaded through kexec_file_load; efifb then traps repeatedly until Hyper-V throttles the guest.

CVSS severity5.5
Medium
EPSS probability0.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Linux hyperv_fb 6.8 allows local users to hang a Hyper-V Gen 2 guest during kdump via a stale framebuffer address. The driver removes conflicting framebuffers after MMIO allocation, allowing relocation while kexec_file_load records the original address in screen_info. Reaching the fault requires an EFI-booted Gen 2 guest, hyperv_fb relocation, and a crash kernel loaded through kexec_file_load; efifb then traps repeatedly until Hyper-V throttles the guest.

The record

CVE
CVE-2025-21977
Published
Apr 1, 2025
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 1, 2025CVE publishedPublication date reported by the CVE source.
  2. May 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=6.8
  2. Affected versionversion=c25a19afb81cfd73dab494ba64f9a434cf1a4499 <2924802d35e00a36b1503a4e786f1926b2fdc1d0
  3. Affected versionversion=c25a19afb81cfd73dab494ba64f9a434cf1a4499 <304386373007aaca9236a3f36afac0bbedcd2bf0
  4. Affected versionversion=c25a19afb81cfd73dab494ba64f9a434cf1a4499 <cfffe46a994ac6d5de3b119917680ea1e9a96125

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=6.8; version=c25a19afb81cfd73dab494ba64f9a434cf1a4499 <2924802d35e00a36b1503a4e786f1926b2fdc1d0; version=c25a19afb81cfd73dab494ba64f9a434cf1a4499 <304386373007aaca9236a3f36afac0bbedcd2bf0; version=c25a19afb81cfd73dab494ba64f9a434cf1a4499 <cfffe46a994ac6d5de3b119917680ea1e9a96125

Published CVSS scores

5.5NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5CanonicalCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5SUSECVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.7SUSECVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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