CVE-2025-37818: debian linux Null Dereference — Fix

Description

In the Linux kernel, the following vulnerability has been resolved: LoongArch: Return NULL from huge_pte_offset() for invalid PMD LoongArch's huge_pte_offset() currently returns a pointer to a PMD slot even if the underlying entry points to invalid_pte_table (indicating no mapping). Callers like smaps_hugetlb_range() fetch this invalid entry value (the address of invalid_pte_table) via this pointer. The generic is_swap_pte() check then incorrectly identifies this address as a swap entry on LoongArch, because it satisfies the "!pte_present() && !pte_none()" conditions. This misinterpretation, combined with a coincidental match by is_migration_entry() on the address bits, leads to kernel crashes in pfn_swap_entry_to_page(). Fix this at the architecture level by modifying huge_pte_offset() to check the PMD entry's content using pmd_none() before returning. If the entry is invalid (i.e., it points to invalid_pte_table), return NULL instead of the pointer to the slot.

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CVSS v3.1 Score

5.5

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-476 CWE-476

Affected Products

Vendor	Product	Versions
linux	linux_kernel	5.19 — 6.1.136
linux	linux_kernel	6.2 — 6.6.89
linux	linux_kernel	6.7 — 6.12.26
linux	linux_kernel	6.13 — 6.14.5
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
debian	debian_linux	All

References

Advisories & Patches

https://git.kernel.org/stable/c/2ca9380b12711afe95b3589bd82b59623b3c96b3 https://git.kernel.org/stable/c/34256805720993e37adf6127371a1265aea8376a https://git.kernel.org/stable/c/51424fd171cee6a33f01f7c66b8eb23ac42289d4 https://git.kernel.org/stable/c/b49f085cd671addbda4802d6b9382513f7dd0f30 https://git.kernel.org/stable/c/bd51834d1cf65a2c801295d230c220aeebf87a73

Other References

https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html

Frequently Asked Questions

What is CVE-2025-37818? +

In the Linux kernel, the following vulnerability has been resolved: LoongArch: Return NULL from huge_pte_offset() for invalid PMD LoongArch's huge_pte_offset() currently returns a pointer to a PMD slot even if the underlying entry points to invalid_pte_table (indicating no mapping). Callers like smaps_hugetlb_range() fetch this invalid entry value (the address of invalid_pte_table) via this pointer. The generic is_swap_pte() check then incorrectly identifies this address as a swap entry on LoongArch, because it satisfies the "!pte_present() && !pte_none()" conditions. This misinterpretation, combined with a coincidental match by is_migration_entry() on the address bits, leads to kernel crashes in pfn_swap_entry_to_page(). Fix this at the architecture level by modifying huge_pte_offset() to check the PMD entry's content using pmd_none() before returning. If the entry is invalid (i.e., it points to invalid_pte_table), return NULL instead of the pointer to the slot. It has a CVSS v3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2025-37818? +

CVE-2025-37818 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2025-37818? +

CVE-2025-37818 affects products from debian, linux, specifically: debian_linux, linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-37818? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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