CVE-2026-63949

/// Technical 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 attrib

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References