CVE-2023-3640

What it actually does

The flaw permits a local user to guess locations within the cpu_entry_area mappings of exception stacks and other per-CPU data despite KASLR and the init_cea_offsets randomization in arch/x86/mm/cpu_entry_area.c, resulting in unauthorized memory reads that can disclose sensitive kernel structures.

Why it matters to the business

Local attackers on affected Linux systems can obtain privileged kernel data and potentially gain full system control, leading to data breaches, service disruption, and costly incident response across server fleets and endpoints.

How an attack unfolds

A local attacker crafts code to probe or infer per-CPU entry area offsets, reads exception stack contents or other mapped data, and uses the disclosed addresses to bypass existing kernel protections and escalate privileges to root.

How to fix it

Apply the latest upstream Linux kernel patches that strengthen cpu_entry_area randomization or backport equivalent fixes; on Red Hat Enterprise Linux, install the corresponding errata kernel packages once available.

How to confirm the fix worked

Verify that the running kernel contains the corrected cpu_entry_area.c logic by checking the kernel version string and confirming the presence of updated init_cea_offsets randomization; test with local proof-of-concept code that attempts offset prediction.

Typical attack path

1. Obtain local user access on a vulnerable Linux host
2. Execute code that enumerates or guesses cpu_entry_area offsets
3. Read sensitive kernel data from exception stacks or per-CPU structures
4. Leverage disclosed addresses to defeat KASLR and escalate privileges

How to detect it

Review system logs for unusual local processes accessing kernel memory mappings; examine auditd or eBPF traces for unexpected reads from cpu_entry_area regions; look for post-exploitation artifacts such as privilege-escalation tools run by low-privileged users.

What your security team should do

• Prioritize kernel updates on all exposed Linux systems within the next maintenance window
• Restrict local user accounts and enforce least-privilege execution where possible
• Monitor kernel mailing lists and vendor advisories for backported fixes
• Enable additional kernel hardening features such as strict page permissions on entry areas