CVE-2022-21505: Oracle Linux Privilege Escalation Flaw

CVE-2022-21505 Overview

CVE-2022-21505 is a Secure Boot Bypass vulnerability in the Linux kernel that affects the Integrity Measurement Architecture (IMA) appraisal mechanism. When IMA appraisal is used with the ima_appraise=log boot parameter, attackers with high privileges can defeat the kernel lockdown security feature using kexec on systems where Secure Boot is disabled or unavailable.

The vulnerability stems from an incomplete security control where IMA prevents setting ima_appraise=log from the boot parameter when Secure Boot is enabled, but this protection does not extend to scenarios where lockdown is used independently of Secure Boot. This creates a security gap that allows privileged attackers to bypass kernel lockdown protections.

Critical Impact

Privileged local attackers can bypass kernel lockdown protections on Linux systems without Secure Boot, potentially loading unsigned kernel code and compromising system integrity.

Affected Products

• Oracle Linux 7
• Oracle Linux 8
• Oracle Linux 9

Discovery Timeline

• 2024-12-24 - CVE CVE-2022-21505 published to NVD
• 2025-06-18 - Last updated in NVD database

Technical Details for CVE-2022-21505

Vulnerability Analysis

This vulnerability (CWE-346: Origin Validation Error) exists in the Linux kernel's handling of the IMA appraisal boot parameter in conjunction with kernel lockdown functionality. The IMA subsystem is designed to verify the integrity of files before they are accessed, while kernel lockdown restricts certain operations that could compromise system integrity.

The flaw occurs because the security check that prevents the ima_appraise=log boot parameter is only enforced when Secure Boot is active. However, kernel lockdown can be enabled independently of Secure Boot on systems where UEFI Secure Boot is either disabled or not supported. In these configurations, an attacker with root privileges can use the kexec system call to load and execute a new kernel image, effectively bypassing the lockdown protections.

The attack requires local access and high privileges (root or equivalent), but successfully exploiting this vulnerability can lead to complete compromise of confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause is an insufficient validation of the trust origin when determining whether to allow the ima_appraise=log boot parameter. The kernel correctly identifies that this parameter should not be allowed when Secure Boot is enabled (since it would undermine the integrity guarantees), but fails to apply the same restriction when lockdown is enabled through other mechanisms.

This represents an incomplete security control where the protection logic assumes Secure Boot is the only mechanism requiring lockdown protections, ignoring alternative configurations where lockdown is enforced independently.

Attack Vector

The attack vector is local and requires the attacker to have high privileges on the target system. The attack proceeds as follows:

1. The attacker gains root access on a Linux system running with kernel lockdown enabled but without Secure Boot
2. The system is configured with ima_appraise=log, which only logs IMA violations rather than enforcing them
3. The attacker leverages kexec to load a modified or unsigned kernel image
4. Since IMA is in logging mode and lockdown checks are bypassed, the new kernel executes without proper validation
5. The attacker now has complete control over the kernel and can execute arbitrary code with kernel privileges

This vulnerability is particularly concerning for systems that rely on kernel lockdown for security hardening in environments where Secure Boot cannot be used, such as certain virtualized environments or legacy hardware.

Detection Methods for CVE-2022-21505

Indicators of Compromise

• Unexpected kexec system calls or kernel reboots without corresponding administrative actions
• IMA log entries showing appraisal failures that were logged but not enforced
• Modified or unsigned kernel images being loaded via kexec
• Unusual root-level processes attempting to interact with kexec functionality

Detection Strategies

• Monitor for kexec system calls using audit subsystem rules targeting the kexec_load and kexec_file_load syscalls
• Review IMA logs for entries indicating ima_appraise=log mode is active on systems with lockdown enabled
• Implement file integrity monitoring on kernel images and bootloader configurations
• Use SentinelOne's kernel-level visibility to detect anomalous kernel loading behavior

Monitoring Recommendations

• Configure auditd rules to alert on kexec-related system calls: auditctl -a always,exit -F arch=b64 -S kexec_load -S kexec_file_load
• Regularly audit boot parameters to ensure ima_appraise=log is not used on systems requiring lockdown
• Monitor /var/log/ima-audit.log or equivalent IMA logging paths for appraisal failures
• Deploy endpoint detection solutions capable of monitoring kernel-level operations

How to Mitigate CVE-2022-21505

Immediate Actions Required

• Review all Linux systems to identify those running with ima_appraise=log boot parameter
• Enable Secure Boot where hardware and configuration allow
• Apply the kernel patch that addresses this vulnerability
• Consider temporarily disabling kexec functionality on critical systems until patched

Patch Information

Oracle has released security updates for Oracle Linux 7, 8, and 9 to address this vulnerability. The Linux kernel commit that resolves this issue ensures that lockdown protections are enforced regardless of whether Secure Boot is enabled.

Administrators should update to the latest kernel version provided by Oracle for their respective Linux distribution version. Refer to the Oracle CVE-2022-21505 Details for specific package versions containing the fix.

Workarounds

• Remove or change the ima_appraise=log boot parameter to ima_appraise=enforce to require strict IMA enforcement
• Disable kexec functionality by setting kernel.kexec_load_disabled=1 via sysctl
• Enable Secure Boot if supported by your hardware and configuration
• Implement additional access controls to restrict root access on affected systems

# Configuration example
# Disable kexec to prevent exploitation
echo "kernel.kexec_load_disabled=1" >> /etc/sysctl.conf
sysctl -p

# Verify IMA appraise mode (should not be 'log' on lockdown systems)
cat /proc/cmdline | grep ima_appraise

# If ima_appraise=log is present, update GRUB configuration
# Edit /etc/default/grub and change ima_appraise=log to ima_appraise=enforce
# Then regenerate GRUB configuration:
grub2-mkconfig -o /boot/grub2/grub.cfg