CVE-2026-63949
Low risk· EPSS 7%Exploitation Probability (EPSS)
Low risk7th percentile - higher than 7% of all known CVEs
Summary
In the Linux kernel, an out-of-bounds (OOB) read vulnerability exists in the auxdisplay line-display driver when writing zero bytes to the 'message' sysfs attribute. The linedisp_display() function reads msg[count - 1] before checking if count is zero, causing a read at msg[-1] which can lead to kernel panic on KASAN-enabled systems or silent adjacent data reads on stock kernels.
Risk Assessment
A local attacker can trigger a kernel panic or potentially leak kernel memory by writing an empty string to the sysfs file. This affects all auxdisplay drivers using linedisp_register()/linedisp_attach(), including ht16k33, max6959, img-ascii-lcd, and seg-led-gpio.
Recommendation
Immediately update the Linux kernel to a version containing the fix (commit that guards against out-of-bounds read). If updating is not possible, temporarily restrict access to sysfs files related to auxdisplay devices.
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Original NVD description (English source)
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.