CVE-2021-3622: Redhat Hivex DOS Vulnerability

CVE-2021-3622 Overview

A stack overflow vulnerability was discovered in the hivex library, which is used for reading and writing Windows Registry hive files. This flaw allows an attacker to provide a specially crafted Windows Registry (hive) file that causes the _get_children() function to recursively call itself without proper depth limits, leading to a stack overflow condition. The vulnerability primarily impacts system availability through denial of service.

Critical Impact

An attacker can crash applications using the hivex library by supplying a maliciously crafted Windows Registry hive file, causing a denial of service condition through uncontrolled recursion in ri-record processing.

Affected Products

• Red Hat Hivex (all versions prior to patch)
• Red Hat Enterprise Linux 6.0, 7.0, and 8.0
• Red Hat Enterprise Linux Workstation 7.0
• Fedora 33 and 34

Discovery Timeline

• 2021-12-23 - CVE-2021-3622 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-3622

Vulnerability Analysis

The vulnerability exists in the hivex library's handling of Windows Registry hive files, specifically within the _get_children() function located in lib/node.c. When processing ri-records (registry index records) within a hive file, the function recursively processes child nodes without enforcing a maximum recursion depth. An attacker can exploit this by creating a malformed hive file with deeply nested or circular ri-record references, causing the function to recurse indefinitely until the stack is exhausted.

The hivex library is commonly used by tools like libguestfs for virtual machine disk image inspection and manipulation. Applications processing untrusted Registry hive files are particularly at risk from this vulnerability.

Root Cause

The root cause is a missing recursion depth limit in the _get_children() function when processing ri-records in Windows Registry hive files. The function did not track or limit the depth of recursive calls, making it susceptible to resource exhaustion attacks via specially crafted input files (CWE-400: Uncontrolled Resource Consumption).

Attack Vector

The attack requires user interaction where a victim must open or process a malicious Windows Registry hive file using an application that relies on the hivex library. The attack is network-deliverable, meaning the malicious file can be distributed via email, web downloads, or shared storage. Once processed, the crafted file triggers uncontrolled recursion in the ri-record parsing logic, exhausting the stack and causing the application to crash.

// Security patch limiting recursion depth in _get_children()
// Source: https://github.com/libguestfs/hivex/commit/771728218dac2fbf6997a7e53225e75a4c6b7255
 
static int _get_children (hive_h *h, hive_node_h blkoff,
                          offset_list *children, offset_list *blocks,
-                          int flags);
+                          int flags, unsigned depth);
static int check_child_is_nk_block (hive_h *h, hive_node_h child, int flags);
 
/* Iterate over children (ie. subkeys of a node), returning child

The patch introduces a depth parameter to the _get_children() function signature, enabling the function to track and limit recursion depth when processing ri-records.

Detection Methods for CVE-2021-3622

Indicators of Compromise

• Unexpected crashes of applications using hivex library during Registry hive file processing
• Stack overflow errors or segmentation faults in processes utilizing hivex functions
• Presence of unusually structured Windows Registry hive files with abnormal ri-record nesting
• Process termination events correlating with hive file operations in libguestfs or similar tools

Detection Strategies

• Monitor for application crashes involving hivex library components or related tools like virt-inspector
• Implement file integrity monitoring for unexpected Registry hive files in processing directories
• Deploy endpoint detection rules to identify stack exhaustion patterns in processes handling hive files
• Configure system logging to capture segmentation faults and abnormal process terminations

Monitoring Recommendations

• Enable crash reporting and core dump analysis for applications utilizing the hivex library
• Monitor system resource usage for unusual stack memory consumption patterns
• Review application logs for hivex-related errors or processing failures
• Implement alerting for repeated crashes of virtualization management tools that use libguestfs

How to Mitigate CVE-2021-3622

Immediate Actions Required

• Update the hivex package to the patched version available from your distribution's repositories
• Apply vendor-provided security updates for Red Hat Enterprise Linux and Fedora systems
• Restrict processing of untrusted Windows Registry hive files until patches are applied
• Review and audit applications that depend on hivex for handling user-supplied files

Patch Information

Red Hat and Fedora have released security updates addressing this vulnerability. The fix was implemented in commit 771728218dac2fbf6997a7e53225e75a4c6b7255 to the hivex repository, which adds a depth parameter to limit recursion in ri-record processing. Administrators should apply updates via their standard package management tools:

• Red Hat Bug Report - Official bug tracking entry
• GitHub Commit for Hivex - Source code fix
• Red Hat Libguestfs Mailing List Announcement - Security advisory

Workarounds

• Avoid processing Windows Registry hive files from untrusted sources until the patch is applied
• Implement application-level sandboxing for hivex-dependent tools to contain potential crashes
• Use process isolation and resource limits (ulimit) to mitigate impact of stack exhaustion
• Consider containerizing applications that process untrusted hive files to limit blast radius

# Apply security updates on Red Hat Enterprise Linux
sudo yum update hivex

# Apply security updates on Fedora
sudo dnf update hivex

# Verify installed hivex version
rpm -q hivex