CVE-2023-3567

What it actually does

Use-after-free in vcs_read within drivers/tty/vt/vc_screen.c allows a local user to access freed kernel memory, resulting in a crash or disclosure of internal kernel information.

Why it matters to the business

Local attackers can trigger system instability causing operational downtime or obtain kernel details that facilitate additional attacks; widespread kernel presence increases exposure across servers and endpoints.

How an attack unfolds

An attacker with local access invokes vcs_read on a virtual console screen device after the underlying memory has been freed, then reads from or writes to the dangling reference to induce a crash or leak sensitive kernel data.

How to fix it

Upgrade the Linux kernel to a version containing the fix for this use-after-free; apply the patch referenced in commit 44f28df24767cf9dca1ddc9b23157737c4cbb645 or later mainline releases that address vc_screen.c.

How to confirm the fix worked

Confirm the running kernel version includes the vc_screen fix, review the source of drivers/tty/vt/vc_screen.c for the corrected vcs_read logic, and test that local access no longer produces crashes or leaks under the prior trigger conditions.

Typical attack path

1. Gain local user access on a Linux system
2. Open or interact with /dev/vcs* or related virtual console interfaces
3. Trigger the race or sequence that frees memory before vcs_read completes
4. Read from or dereference the freed object to crash the kernel or extract data

How to detect it

Review kernel logs and dmesg for oops/panic messages referencing vc_screen or vcs_read; inspect audit logs for unusual access to virtual console devices by non-privileged users.

What your security team should do

• Prioritize kernel updates on all affected Linux distributions and embedded devices
• Limit local user privileges and console access where feasible
• Monitor kernel logs for oops or panic entries involving vc_screen
• Harden systems against local privilege-escalation chains that could leverage this flaw