CVE-2026-63949

Description

In the Linux kernel, the following vulnerability has been resolved: auxdisplay: line-display: fix OOB read on zero-length message_store() linedisp_display() unconditionally reads msg[count - 1] before checking whether count is zero, so a write of zero bytes to the message sysfs attribute hits msg[-1]: write(fd, "", 0); -> message_store(..., buf, count=0) -> linedisp_display(linedisp, buf, count=0) -> msg[count - 1] == '\n' ; OOB read The kernfs write buffer for that store is a 1-byte allocation (kernfs_fop_write_iter() does kmalloc(len + 1) with len == 0), so msg[-1] is a 1-byte read before the slab object. On a KASAN-enabled kernel this trips an out-of-bounds report and panics; on stock kernels it silently reads adjacent slab data and, if that byte happens to be '\n', the following count-- wraps ssize_t 0 to -1 and is then passed to kmemdup_nul(). linedisp_display() is reached from the message_store() sysfs callback (drivers/auxdisplay/line-display.c message attribute, mode 0644) and from the in-tree initial-message setup with count == -1, so the OOB path is only userspace-triggerable via zero-byte writes; vfs_write() does not short-circuit on count == 0 and kernfs_fop_write_iter() dispatches the store callback regardless. Guard the trailing-newline trim with a count check. The existing if (!count) block then takes the clear-display path unchanged. Affects every auxdisplay driver that registers via linedisp_register() / linedisp_attach(): ht16k33, max6959, img-ascii-lcd, seg-led-gpio.

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Patch details

References

• MITRE
• NVD
• Launchpad
• Debian

Related Ubuntu Security Notices (USN)

• USN-8593-1
• Linux kernel vulnerabilities
• 23 July 2026
• USN-8603-1
• Linux kernel (Azure) vulnerabilities
• 24 July 2026
• USN-8618-1
• Linux kernel vulnerabilities
• 28 July 2026

Other references

• https://www.cve.org/CVERecord?id=CVE-2026-63949
• https://git.kernel.org/linus/a7511dcd9dd4bc55d123f9b800c8a4ed2662e5c6 (7.1-rc7)