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CVE-2025-40322: fbdev: bitblit: bound-check glyph index in bit_putcs*

• Severity: high (CVSS 7.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-12-08 · updated 2026-10-14

Description

In the Linux kernel, the following vulnerability has been resolved: fbdev: bitblit: bound-check glyph index in bit_putcs* bit_putcs_aligned()/unaligned() derived the glyph pointer from the character value masked by 0xff/0x1ff, which may exceed the actual font's glyph count and read past the end of the built-in font array. Clamp the index to the actual glyph count before computing the address. This fixes a global out-of-bounds read reported by syzbot.

Affected products

• Linux kernel: 2.6.12 — fixed in 6.18

How to fix

Upgrade to a fixed version: Linux kernel 6.18. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/0998a6cb232674408a03e8561dc15aa266b2f53b
• https://git.kernel.org/stable/c/18c4ef4e765a798b47980555ed665d78b71aeadf
• https://git.kernel.org/stable/c/901f44227072be60812fe8083e83e1533c04eed1
• https://git.kernel.org/stable/c/9ba1a7802ca9a2590cef95b253e6526f4364477f
• https://git.kernel.org/stable/c/a10cede006f9614b465cf25609a8753efbfd45cc
• https://git.kernel.org/stable/c/c12003bf91fdff381c55ef54fef3e961a5af2545
• https://git.kernel.org/stable/c/db5c9a162d2f42bcc842b76b3d935dcc050a0eec
• https://git.kernel.org/stable/c/efaf89a75a29b2d179bf4fe63ca62852e93ad620

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