CVE-2021-3411: Linux Kernel Information Disclosure Flaw

CVE-2021-3411 Overview

A memory access violation flaw was discovered in the Linux kernel in versions prior to 5.10. The vulnerability occurs during the detection of int3 (interrupt 3) padding in the linking state, potentially allowing a local attacker with elevated privileges to compromise data confidentiality, integrity, and system availability. This kernel vulnerability affects the code injection protection mechanisms and could be exploited to undermine security controls.

Critical Impact

A local attacker with high privileges can exploit this memory access violation to potentially read or modify sensitive kernel data and cause system instability, impacting confidentiality, integrity, and availability.

Affected Products

• Linux Kernel versions prior to 5.10
• Red Hat Enterprise Linux 8.0
• Systems running vulnerable kernel versions with int3 padding detection

Discovery Timeline

• 2021-03-09 - CVE CVE-2021-3411 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-3411

Vulnerability Analysis

This vulnerability represents a memory access violation (CWE-94: Improper Control of Generation of Code) that occurs within the Linux kernel's handling of int3 padding during the linking process. Int3 instructions (opcode 0xCC) are commonly used as software breakpoints and for code alignment padding. The flaw manifests when the kernel improperly accesses memory while detecting these int3 padding sequences during the linking state of kernel modules or code sections.

The vulnerability requires local access and high privileges to exploit, which limits the attack surface. However, successful exploitation could allow an attacker to achieve arbitrary code execution within kernel context, potentially leading to complete system compromise.

Root Cause

The root cause of this vulnerability lies in improper boundary checking or memory access validation within the kernel's int3 padding detection mechanism. During the linking process, the kernel must scan and identify int3 instruction padding, but a flaw in this detection logic allows out-of-bounds memory access. This could result in reading or writing to unintended memory locations, compromising the integrity of kernel data structures.

Attack Vector

The attack requires local access to the target system with elevated privileges. An attacker would need to trigger the vulnerable code path during the kernel's linking operations. This could potentially be achieved through:

The vulnerability is exploited locally where an attacker with high-level privileges initiates operations that trigger the kernel's int3 padding detection mechanism during the linking state. The improper memory access can then be leveraged to read sensitive kernel memory, modify kernel data structures, or cause system instability. Since int3 instructions are integral to debugging and code protection mechanisms, this vulnerability could potentially be used to bypass security controls implemented using these instructions.

Detection Methods for CVE-2021-3411

Indicators of Compromise

• Unexpected kernel panics or system crashes during module loading or linking operations
• Anomalous memory access patterns in kernel space detected by monitoring tools
• Suspicious privileged process activity involving kernel module operations
• Kernel oops messages referencing int3 or linking-related functions

Detection Strategies

• Monitor kernel logs for memory access violation errors related to linking operations
• Implement kernel-level auditing to track module loading and linking activities
• Deploy endpoint detection solutions capable of monitoring kernel-level behavior
• Use SentinelOne's Singularity platform to detect anomalous kernel activity patterns

Monitoring Recommendations

• Enable comprehensive kernel logging with dmesg monitoring for memory-related errors
• Configure auditd rules to track privileged operations and module loading events
• Deploy real-time kernel integrity monitoring solutions
• Implement alerting for unexpected system crashes or kernel panics

How to Mitigate CVE-2021-3411

Immediate Actions Required

• Update the Linux kernel to version 5.10 or later to address the vulnerability
• Apply vendor-specific patches from Red Hat for Enterprise Linux 8.0 systems
• Restrict local access and privilege escalation paths to minimize attack surface
• Monitor systems for signs of exploitation attempts

Patch Information

Organizations should upgrade their Linux kernel to version 5.10 or later, which contains the fix for this memory access violation. Red Hat users should consult the Red Hat Bug Report for Enterprise Linux 8.0-specific patch information. Additional technical details about the vulnerability are available in the Pi3 Blog Post.

Workarounds

• Limit local user access and enforce strict privilege separation to reduce exposure
• Implement kernel module signing and loading restrictions where possible
• Monitor and audit privileged user activities on affected systems
• Consider kernel hardening options such as lockdown mode where applicable

# Example: Check current kernel version and update
uname -r
# Update kernel on RHEL/CentOS systems
sudo yum update kernel
# Reboot to apply new kernel
sudo reboot