CVE-2026-74439 iommu/vt-d: Clear Present bit before tearing down scalable-mode context entry
A race condition in Linux kernel IOMMU teardown allows hardware to access freed memory, potentially causing system crashes or unpredictable behavior.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-74439?
CVE-2026-74439 is a critical vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
iommu/vt-d: Clear Present bit before tearing down scalable-mode context entry
device_pasid_table_teardown() zeroes the 128-bit scalable-mode context entry with context_clear_entry() while the Present bit is still set. This creates a window where the hardware can fetch a torn entry, with some fields already zeroed while Present is still set, leading to unpredictable behavior or spurious faults. The context-cache invalidation is issued only after the entry has been zeroed, and intel_pasid_free_table() then frees the PASID directory pages, so the IOMMU can keep walking a stale Present=1 entry that points at freed memory.
While x86 provides strong write ordering, the compiler may reorder the two 64-bit writes to the entry, and the hardware fetch is not guaranteed to be atomic with respect to multiple CPU writes.
Commit c1e4f1dccbe9d ("iommu/vt-d: Clear Present bit before tearing down context entry") fixed this exact pattern in domain_context_clear_one() and the copied-context path, but device_pasid_table_teardown() was not converted.
Align it with the "Guidance to Software for Invalidations" in the VT-d spec, Section 6.5.3.3, using the same ownership handshake as the sibling fix: clear only the Present bit, flush it to the IOMMU, perform the context-cache invalidation, and only then zero the rest of the entry.
Which versions are affected by CVE-2026-74439?
How do I fix CVE-2026-74439?
Apply the vendor's patch.
Is CVE-2026-74439 being exploited?
There is no known exploitation of CVE-2026-74439 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-74439, DEBIAN-CVE-2026-74439, GHSA-3r9j-57rx-vfgp, UBUNTU-CVE-2026-74439.