CVE-2026-63875
HIGHarm64: tlb: Flush walk cache when unsharing PMD tables
Blast Radius
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Description
In the Linux kernel, the following vulnerability has been resolved:
arm64: tlb: Flush walk cache when unsharing PMD tables
When huge_pmd_unshare() is called to unshare a PMD table, the tlb_unshare_pmd_ptdesc() function sets tlb->unshared_tables=true but the aarch64 tlb_flush() only checked tlb->freed_tables to determine whether to use TLBF_NONE (vae1is, invalidates walk cache) or TLBF_NOWALKCACHE (vale1is, leaf-only).
This caused the stale PMD page table entry to remain in the walk cache after unshare, potentially leading to incorrect page table walks.
Fix by including unshared_tables in the check, so that when unsharing tables, TLBF_NONE is used and the walk cache is properly invalidated.
Here is the detailed distinction between vae1is and vale1is:
| Instruction Combination | Actual Invalidation Scope |
|---|---|
VAE1IS + TTL=0 | All entries at all levels (full invalidation) |
VAE1IS + TTL=2 (L2) | Non-leaf at Level 0/1 + leaf at Level 2 |
VALE1IS + TTL=0 | Leaf entries at all levels (non-leaf not cleared) |
VALE1IS + TTL=2 (L2) | Leaf entry at Level 2 only |
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐧Linux | Kernel | ≥ 5.11.0&&< 5.10.259 | 5.10.259 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Kernel. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update Kernel to 5.10.259 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-63875 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-63875 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-63875. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-63875 in your dependencies?
O3 detects CVE-2026-63875 across Linux dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.