CVE-2021-3802: Udisks2 Denial of Service Vulnerability

CVE-2021-3802 Overview

CVE-2021-3802 is an Improper Input Validation vulnerability discovered in udisks2, a daemon that provides interfaces for managing storage devices on Linux systems. This flaw allows an attacker to input a specially crafted image file or USB device, which can lead to a kernel panic. The vulnerability primarily impacts system availability, potentially causing complete denial of service on affected systems.

Critical Impact

A local attacker with high privileges can trigger a kernel panic through specially crafted storage media, causing complete system unavailability and requiring manual intervention to restore services.

Affected Products

• udisks_project udisks (all versions prior to fix)
• Fedora 34
• Red Hat Enterprise Linux 8.0

Discovery Timeline

• 2021-11-29 - CVE-2021-3802 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-3802

Vulnerability Analysis

The vulnerability resides in udisks2's handling of storage device media. When processing specially crafted image files or USB devices, udisks2 fails to properly validate input data before passing it to kernel-level operations. This improper input validation (CWE-20) allows malicious input to propagate through the system, ultimately triggering a kernel panic condition.

The attack requires local access to the system and high privileges to execute. User interaction is also required, typically involving mounting or interacting with the malicious storage media. While the vulnerability does not compromise data confidentiality or integrity, it poses a significant threat to system availability.

Root Cause

The root cause of CVE-2021-3802 is improper input validation in the udisks2 daemon when processing filesystem metadata from storage devices. The daemon fails to adequately sanitize and validate data structures from mounted media before invoking kernel-level mount operations. When a maliciously crafted image file or USB device contains malformed metadata, this unvalidated input triggers undefined behavior in the kernel, resulting in a panic condition.

Attack Vector

The attack vector for this vulnerability is local, requiring an attacker to have physical access to the system or the ability to present a malicious image file to the udisks2 daemon. The exploitation scenario typically involves:

1. An attacker prepares a specially crafted disk image or USB device with malformed filesystem metadata
2. The attacker presents this storage media to a vulnerable system running udisks2
3. When the system attempts to enumerate or mount the device through udisks2, the malformed data is processed
4. The unvalidated input reaches kernel-level operations, triggering a kernel panic
5. The system becomes completely unavailable until manually rebooted

The vulnerability mechanism involves improper boundary checking and input sanitization in udisks2's device handling routines. For detailed technical information, refer to the SYSS Security Advisory #045 and the Red Hat Bug Report #2003649.

Detection Methods for CVE-2021-3802

Indicators of Compromise

• Unexpected kernel panic events with crash logs referencing storage device operations or udisks2
• System reboots occurring immediately after USB device insertion or disk image mounting
• Kernel log entries showing errors in filesystem parsing or mount operations preceding system crashes
• Crash dump analysis revealing udisks2 or storage-related kernel modules in the call stack

Detection Strategies

• Monitor system logs for kernel panic events and correlate with recent storage device activity
• Implement USB device insertion monitoring to track all new storage media connections
• Deploy endpoint detection rules that alert on unexpected system reboots following device mount operations
• Configure SentinelOne Singularity Platform to detect anomalous udisks2 behavior patterns

Monitoring Recommendations

• Enable kernel crash dump collection to facilitate post-incident analysis of panic events
• Configure centralized logging to capture dmesg output and system journal entries related to storage operations
• Monitor for repeated system crashes that may indicate active exploitation attempts
• Deploy file integrity monitoring on udisks2 configuration files and binaries

How to Mitigate CVE-2021-3802

Immediate Actions Required

• Update udisks2 packages to the latest patched versions available from your distribution
• Restrict USB device access to authorized users only through udev rules
• Implement USB device whitelisting to prevent mounting of unknown storage media
• Consider disabling automatic mounting of removable media on critical systems

Patch Information

Vendors have released patches addressing this vulnerability. Administrators should apply updates from their respective Linux distributions:

• Red Hat Enterprise Linux: Refer to Red Hat Bug Report #2003649 for patch information
• Debian/Ubuntu: Check the Debian LTS Security Announcement for patched package versions
• Fedora: Update udisks2 packages through standard package management

Verify patch installation by checking the udisks2 package version against your distribution's security advisories.

Workarounds

• Configure udev rules to restrict USB storage device access to specific trusted users or groups
• Disable automatic mounting by configuring udisks2 to require explicit user authentication for mount operations
• Implement physical USB port restrictions where feasible in high-security environments
• Use application whitelisting to control which processes can interact with storage device interfaces

# Configuration example - Restrict USB storage mounting via udev rules
# Create /etc/udev/rules.d/99-usb-storage-restrict.rules
ACTION=="add", SUBSYSTEM=="block", KERNEL=="sd*", ATTRS{removable}=="1", GROUP="storage", MODE="0660"

# Reload udev rules after creation
sudo udevadm control --reload-rules
sudo udevadm trigger