CVE-2025-39967: fbcon: fix integer overflow in fbcon_do_set_font

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-10-15 · updated 2026-10-19
Weakness: CWE-190

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.

Affected products

Linux kernel: from 4.4.235 before 4.5; from 4.9.235 before 4.10; from 4.14.196 before 4.15; from 4.19.143 before 4.20; from 5.4.62 before 5.4.300; from 5.8.6 before 5.9 — fixed in 4.10, 4.15, 4.20, 4.5, 5.10.245, 5.15.194

How to fix

Upgrade to a fixed version: Linux kernel 4.10, 4.15, 4.20, 4.5. Check the vendor advisory for mitigations.

References

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