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CVE Record

CVE-2025-21976: fbdev: hyperv_fb: Allow graceful removal of framebuffer

In the Linux kernel, the following vulnerability has been resolved: fbdev: hyperv_fb: Allow graceful removal of framebuffer When a Hyper-V framebuffer device is unbind, hyperv_fb driver tries to release the framebuffer forcefully. If this framebuffer is in use it produce the following WARN and hence this framebuffer is never released. [ 44.111220] WARNING: CPU: 35 PID: 1882 at drivers/video/fbdev/core/fb_info.c:70 framebuffer_release+0x2c/0x40 < snip > [ 44.111289] Call Trace: [ 44.111290] <TASK> [ 44.111291] ? show_regs+0x6c/0x80 [ 44.111295] ? __warn+0x8d/0x150 [ 44.111298] ? framebuffer_release+0x2c/0x40 [ 44.111300] ? report_bug+0x182/0x1b0 [ 44.111303] ? handle_bug+0x6e/0xb0 [ 44.111306] ? exc_invalid_op+0x18/0x80 [ 44.111308] ? asm_exc_invalid_op+0x1b/0x20 [ 44.111311] ? framebuffer_release+0x2c/0x40 [ 44.111313] ? hvfb_remove+0x86/0xa0 [hyperv_fb] [ 44.111315] vmbus_remove+0x24/0x40 [hv_vmbus] [ 44.111323] device_remove+0x40/0x80 [ 44.111325] device_release_driver_internal+0x20b/0x270 [ 44.111327] ? bus_find_device+0xb3/0xf0 Fix this by moving the release of framebuffer and assosiated memory to fb_ops.fb_destroy function, so that framebuffer framework handles it gracefully. While we fix this, also replace manual registrations/unregistration of framebuffer with devm_register_framebuffer.

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This Linux kernel flaw affects Hyper-V framebuffer cleanup. If the framebuffer device is removed while in use, the driver can trigger a kernel warning and fail to release it. The supplied record rates it 7.8 high, although the sources do not demonstrate data theft, privilege escalation, or remote compromise.

Executive priority

Use an accelerated maintenance cycle for confirmed Hyper-V Linux guests, particularly systems accessible to untrusted local users. This is a high-rated issue, but the provided evidence does not support emergency incident response or claims of active exploitation. Deprioritize systems that are not Hyper-V guests or do not use hyperv_fb.

Technical view

During hyperv_fb device unbinding, hvfb_remove forcefully releases an in-use framebuffer, causing a warning in framebuffer_release and preventing release. The fix moves framebuffer and associated-memory cleanup into fb_ops.fb_destroy so the framebuffer framework manages teardown, and replaces manual registration with devm_register_framebuffer.

Likely exposure

Exposure is limited to Linux systems using the Hyper-V framebuffer driver. The problematic condition requires framebuffer device unbinding or removal while the framebuffer remains in use. The supplied affected-version data is ambiguous, so organizations should map their exact kernel package against vendor guidance or the referenced stable fixes.

Exploitation context

The supplied sources provide no evidence of active exploitation, and the CVE is not identified as KEV. The vector describes local, low-privilege access without user interaction, but the published technical description documents faulty teardown, a warning, and incomplete resource release rather than a demonstrated compromise path.

Researcher notes

No CWE is assigned. The source describes an improper framebuffer teardown and cleanup-lifecycle defect. Three stable-kernel commits are referenced, but the bundle does not map each commit to a specific release branch. The listed affected versions contain ambiguous entries, including “0,” so package-level conclusions require vendor confirmation.

Mitigation direction

  • Update to a kernel package containing the applicable upstream stable fix.
  • Confirm the fixed package with the Linux distribution or cloud-platform vendor.
  • Until updated, avoid unnecessary Hyper-V framebuffer device unbinding on production guests.
  • Prioritize affected multi-user or otherwise untrusted Linux guests.

Validation and detection

  • Confirm whether each Linux workload runs as a Hyper-V guest.
  • Determine whether the hyperv_fb driver and Hyper-V framebuffer device are present.
  • Compare the installed kernel build with vendor advisories and referenced stable fixes.
  • Review kernel logs for warnings involving framebuffer_release, hvfb_remove, or hyperv_fb.
  • In a controlled guest, verify framebuffer removal completes without the documented warning.
Prepared
Confidence
medium
Sources
5

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2025-21976 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
0ADP providers
4Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.8CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H1.85.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.8High
CVSS 3.1 vector shape for CVE-2025-21976Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux68a2d20b79b105f02dcbc52c211d7e62f98996b7, 68a2d20b79b105f02dcbc52c211d7e62f98996b7, 68a2d20b79b105f02dcbc52c211d7e62f98996b7unaffected
LinuxLinux3.10, 0, 6.12.20, 6.13.8, 6.14affected
Weakness

CWE details

No CWE listed

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