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CVE Record

CVE-2025-21876: iommu/vt-d: Fix suspicious RCU usage

In the Linux kernel, the following vulnerability has been resolved: iommu/vt-d: Fix suspicious RCU usage Commit <d74169ceb0d2> ("iommu/vt-d: Allocate DMAR fault interrupts locally") moved the call to enable_drhd_fault_handling() to a code path that does not hold any lock while traversing the drhd list. Fix it by ensuring the dmar_global_lock lock is held when traversing the drhd list. Without this fix, the following warning is triggered: ============================= WARNING: suspicious RCU usage 6.14.0-rc3 #55 Not tainted ----------------------------- drivers/iommu/intel/dmar.c:2046 RCU-list traversed in non-reader section!! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 1 2 locks held by cpuhp/1/23: #0: ffffffff84a67c50 (cpu_hotplug_lock){++++}-{0:0}, at: cpuhp_thread_fun+0x87/0x2c0 #1: ffffffff84a6a380 (cpuhp_state-up){+.+.}-{0:0}, at: cpuhp_thread_fun+0x87/0x2c0 stack backtrace: CPU: 1 UID: 0 PID: 23 Comm: cpuhp/1 Not tainted 6.14.0-rc3 #55 Call Trace: <TASK> dump_stack_lvl+0xb7/0xd0 lockdep_rcu_suspicious+0x159/0x1f0 ? __pfx_enable_drhd_fault_handling+0x10/0x10 enable_drhd_fault_handling+0x151/0x180 cpuhp_invoke_callback+0x1df/0x990 cpuhp_thread_fun+0x1ea/0x2c0 smpboot_thread_fn+0x1f5/0x2e0 ? __pfx_smpboot_thread_fn+0x10/0x10 kthread+0x12a/0x2d0 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x4a/0x60 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK> Holding the lock in enable_drhd_fault_handling() triggers a lockdep splat about a possible deadlock between dmar_global_lock and cpu_hotplug_lock. This is avoided by not holding dmar_global_lock when calling iommu_device_register(), which initiates the device probe process.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2025-21876 is a Linux kernel Intel IOMMU/VT-d locking bug. A kernel path could traverse a shared DMAR hardware list without the required lock, triggering suspicious RCU usage warnings. The supplied sources do not show active exploitation, CVSS scoring, or business impact beyond kernel correctness and stability risk.

Executive priority

Treat as a normal kernel maintenance item unless critical workloads show related kernel warnings or vendor advisories raise severity. Patch through standard OS update channels after testing, with higher priority for virtualization hosts and hardware-dependent infrastructure.

Technical view

The issue was introduced when enable_drhd_fault_handling() moved into a path that did not hold dmar_global_lock while walking the drhd list. The fix ensures the lock is held for traversal while avoiding a lockdep deadlock with cpu_hotplug_lock by changing where iommu_device_register() runs.

Likely exposure

Exposure appears limited to Linux systems running affected kernel builds with Intel VT-d/IOMMU code paths. The source bundle lists Linux kernel versions and upstream stable fixes, but does not provide distribution-specific package names or complete platform conditions.

Exploitation context

No active exploitation is cited. The CVE is not listed as KEV in the supplied bundle, and the references describe a kernel warning and locking correction, not a public exploit or attacker workflow.

Researcher notes

Evidence supports a concurrency/locking defect in drivers/iommu/intel/dmar.c. The available record lacks CVSS, CWE, exploitability analysis, and distribution impact. Validate exposure by matching deployed kernels to vendor backports rather than relying only on upstream version numbers.

Mitigation direction

  • Check vendor kernel advisories for CVE-2025-21876 coverage.
  • Update to a vendor-supported kernel containing the upstream stable fixes.
  • Prioritize systems using Intel VT-d/IOMMU or virtualization features.
  • Do not deploy custom kernel patches without normal regression testing.

Validation and detection

  • Inventory Linux kernel versions across servers and appliances.
  • Confirm whether Intel VT-d/IOMMU is enabled on relevant systems.
  • Check vendor changelogs for CVE-2025-21876 or the referenced commits.
  • Review kernel logs for suspicious RCU or DMAR-related warnings.
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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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
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.

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

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

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Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxd74169ceb0d2e32438946a2f1f9fc8c803304bd6, d74169ceb0d2e32438946a2f1f9fc8c803304bd6, d74169ceb0d2e32438946a2f1f9fc8c803304bd6unaffected
LinuxLinux6.10, 0, 6.12.18, 6.13.6, 6.14affected
Weakness

CWE details

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