CVE-2022-4543: Linux Kernel Information Disclosure Flaw

CVE-2022-4543 Overview

CVE-2022-4543, named "EntryBleed," is an information disclosure vulnerability discovered in the Linux Kernel Page Table Isolation (KPTI) implementation. This flaw enables a local attacker to bypass Kernel Address Space Layout Randomization (KASLR) protections by exploiting prefetch side-channels based on TLB (Translation Lookaside Buffer) timing on Intel-based systems. By leveraging this vulnerability, attackers can leak the KASLR base address, which significantly weakens kernel memory protection mechanisms and potentially facilitates further exploitation of other kernel vulnerabilities.

Critical Impact

Local attackers can leak kernel base addresses via timing-based side-channel attacks, undermining KASLR protections and enabling more sophisticated kernel exploitation chains.

Affected Products

• Linux Kernel (all versions prior to patch)
• Intel-based systems running vulnerable Linux kernel versions
• Systems with KPTI (Kernel Page Table Isolation) enabled

Discovery Timeline

• 2023-01-11 - CVE CVE-2022-4543 published to NVD
• 2025-04-08 - Last updated in NVD database

Technical Details for CVE-2022-4543

Vulnerability Analysis

The EntryBleed vulnerability (CWE-200: Exposure of Sensitive Information, CWE-203: Observable Discrepancy) resides in the Linux Kernel's Page Table Isolation mechanism. KPTI was originally implemented as a mitigation against Meltdown attacks by separating kernel and user-space page tables. However, this implementation contains a flaw that allows local attackers to infer the kernel's base address through timing analysis.

The vulnerability exploits observable timing differences in TLB (Translation Lookaside Buffer) operations when accessing memory. By measuring prefetch timing variations, an attacker can distinguish between valid and invalid kernel addresses, effectively derandomizing KASLR. This is particularly concerning because KASLR serves as a fundamental defense mechanism that randomizes the location of kernel code and data in memory to prevent exploitation of memory corruption vulnerabilities.

Root Cause

The root cause of EntryBleed lies in the incomplete isolation of kernel page table entries within the KPTI implementation. When a local process performs prefetch operations, the CPU's TLB caching behavior creates measurable timing differences that correlate with the validity of kernel virtual addresses. These timing side-channels leak information about which kernel addresses are mapped, allowing an attacker to deduce the randomized kernel base address.

The vulnerability specifically affects Intel processors where prefetch timing behavior is predictable enough to exploit. The KPTI implementation failed to adequately prevent these timing-based information leaks, leaving a gap in the kernel's defense-in-depth strategy.

Attack Vector

This is a local attack vector requiring the attacker to have local access to the target system with standard user privileges. The attack methodology involves:

1. Timing Measurement Setup: The attacker creates a timing measurement framework to detect nanosecond-level differences in memory access operations.

2. Prefetch Probing: The attacker systematically issues prefetch instructions targeting various kernel address ranges.

3. TLB Timing Analysis: By measuring the timing of prefetch operations, the attacker identifies which addresses produce timing patterns consistent with valid kernel mappings.

4. KASLR Base Derivation: Through statistical analysis of collected timing data, the attacker reconstructs the randomized kernel base address.

The attack requires no user interaction and can be executed by any local user with standard privileges. For detailed technical analysis, refer to the Willsroot EntryBleed Analysis.

Detection Methods for CVE-2022-4543

Indicators of Compromise

• Unusual patterns of prefetch instruction usage from user-space processes
• Processes performing systematic memory address probing across kernel address ranges
• Elevated CPU utilization from timing measurement operations
• Processes accessing hardware performance counters for cycle-accurate timing

Detection Strategies

• Monitor for processes making excessive use of prefetch instructions via kernel audit subsystem
• Implement behavioral analysis to detect timing side-channel attack patterns
• Deploy SentinelOne Singularity platform for real-time detection of kernel exploitation attempts
• Enable kernel auditing to track suspicious memory access patterns from user-space

Monitoring Recommendations

• Enable kernel tracing with perf or ftrace to monitor prefetch instruction patterns
• Implement security monitoring for processes accessing /proc/kallsyms or attempting to read kernel symbol information
• Deploy endpoint detection solutions capable of identifying side-channel attack behavior
• Review system logs for anomalous process behavior indicative of kernel address probing

How to Mitigate CVE-2022-4543

Immediate Actions Required

• Update Linux kernel to the latest patched version that addresses EntryBleed
• Review system configurations to ensure KASLR is properly configured
• Monitor for exploitation attempts using behavioral detection tools
• Assess exposure of Intel-based systems running vulnerable kernel versions

Patch Information

Linux kernel maintainers have released patches to address the EntryBleed vulnerability. Organizations should update their Linux kernel to the latest stable version that includes fixes for CVE-2022-4543. For detailed information about the vulnerability disclosure and patch status, refer to the Openwall OSS Security Discussion.

Administrators should prioritize patching systems where local users have shell access, as this vulnerability requires local access to exploit.

Workarounds

• Restrict local shell access to trusted users only to reduce attack surface
• Consider additional kernel hardening measures such as enabling kptr_restrict to hide kernel pointers
• Deploy application sandboxing to limit the ability of user processes to perform timing attacks
• On highly sensitive systems, consider disabling SMT (Simultaneous Multithreading) as an additional defense against timing side-channels

# Configuration example
# Restrict kernel pointer exposure
echo 2 > /proc/sys/kernel/kptr_restrict

# Verify KASLR is enabled (should be enabled by default)
cat /proc/cmdline | grep -i kaslr

# Check current kernel version and update if needed
uname -r
apt update && apt upgrade linux-image-generic  # Debian/Ubuntu
# or
yum update kernel  # RHEL/CentOS