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

> A kernel panic occurs on nios2 systems with FLATMEM due to incorrect memory limit calculations, causing a denial of service.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 4 Dec 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-40245, DEBIAN-CVE-2025-40245, GHSA-56rc-pfj3-9mx3, ROOT-OS-DEBIAN-11-CVE-2025-40245, ROOT-OS-UBUNTU-2404-CVE-2025-40245, UBUNTU-CVE-2025-40245

## What is CVE-2025-40245?

CVE-2025-40245 is a high-severity denial of service vulnerability in Linux, published on 4 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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.

## Which versions are affected by CVE-2025-40245?


## How do I fix CVE-2025-40245?

Apply the vendor's patch.

## Is CVE-2025-40245 being exploited?

There is no known exploitation of CVE-2025-40245 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40245 and fix it if it is affected.

What it is: CVE-2025-40245 is a high-severity denial of service vulnerability in Linux, published on 4 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-40245 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-40245/ (Markdown: https://insights.sbomify.com/CVE-2025-40245/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40245
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40245
- OSV: https://osv.dev/vulnerability/CVE-2025-40245

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40245/
Summaries are generated and may contain mistakes; the official description above is the record.