CVE-2020-35457: Gnome GLib Buffer Overflow Vulnerability

CVE-2020-35457 Overview

CVE-2020-35457 is an integer overflow vulnerability in GNOME GLib before version 2.65.3, specifically within the g_option_group_add_entries() function. This vulnerability could potentially lead to an out-of-bounds write condition. While the GNOME vendor has noted that the standard usage pattern involves static option entry lists which limits real-world exploitability, the vulnerability represents a concerning memory safety issue in a widely-used foundational library.

Critical Impact

An integer overflow in g_option_group_add_entries() may result in out-of-bounds memory writes, potentially enabling arbitrary code execution with local access.

Affected Products

• GNOME GLib versions prior to 2.65.3

Discovery Timeline

• 2020-12-14 - CVE-2020-35457 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-35457

Vulnerability Analysis

The vulnerability exists in the g_option_group_add_entries() function within GNOME GLib. This function is responsible for adding command-line option entries to an option group. The integer overflow occurs during calculations related to entry management, which can cause the allocated buffer size to be smaller than expected. When subsequent write operations occur, they may exceed the actual buffer boundaries, resulting in an out-of-bounds write condition.

GLib is a foundational library used extensively across the GNOME desktop environment and many Linux applications. The g_option_group_add_entries() function is commonly used by applications to handle command-line argument parsing. While the GNOME project has stated that typical usage patterns involve static lists passed in a fixed number of calls (limiting practical exploitation), the security researcher who reported the issue noted this pattern is undocumented, meaning developers may unknowingly introduce vulnerable code paths.

The local attack vector requires an attacker to have some level of access to the target system, though the low complexity of the attack means that once local access is obtained, exploitation may be straightforward.

Root Cause

The root cause is an integer overflow vulnerability (CWE-190) in the g_option_group_add_entries() function. When processing a large number of option entries, integer arithmetic used for memory allocation calculations can overflow, resulting in an undersized buffer allocation. This creates a classic out-of-bounds write scenario where subsequent operations write data beyond the allocated memory region.

Attack Vector

The attack requires local access to exploit. An attacker with local privileges could craft malicious input that triggers the integer overflow condition in g_option_group_add_entries(). The exploitation involves:

1. Providing carefully crafted option entries that cause the integer calculation to overflow
2. The resulting memory allocation is smaller than required
3. Subsequent writes to the undersized buffer corrupt adjacent memory
4. This memory corruption could potentially be leveraged for arbitrary code execution

The vulnerability mechanism involves mathematical overflow in size calculations passed to memory allocation routines. When the calculated size wraps around due to integer overflow, the allocated buffer is insufficient for the data being written, leading to heap corruption. For detailed technical analysis, see the GNOME glib Issue #2197.

Detection Methods for CVE-2020-35457

Indicators of Compromise

• Unexpected crashes in applications linked against GLib, particularly during command-line argument parsing
• Memory corruption errors or segmentation faults in GLib-dependent applications
• Anomalous memory allocation patterns in processes using the g_option_group_add_entries() function

Detection Strategies

• Monitor for unexpected application crashes that indicate potential memory corruption
• Implement memory debugging tools (AddressSanitizer, Valgrind) in development environments to detect out-of-bounds writes
• Audit applications that dynamically add large numbers of option entries using GLib functions
• Track GLib library versions across systems to identify vulnerable installations

Monitoring Recommendations

• Inventory all systems running GLib versions prior to 2.65.3
• Monitor system logs for segmentation faults or memory-related errors in GLib-dependent applications
• Implement centralized crash reporting to correlate potential exploitation attempts
• Use SentinelOne's endpoint detection capabilities to identify anomalous process behavior

How to Mitigate CVE-2020-35457

Immediate Actions Required

• Upgrade GNOME GLib to version 2.65.3 or later immediately
• Review applications that use g_option_group_add_entries() with dynamic or user-influenced option lists
• Apply operating system updates that include patched GLib packages
• Restrict local access to systems running vulnerable GLib versions where upgrading is not immediately possible

Patch Information

GNOME has addressed this vulnerability in GLib version 2.65.3. The fix is available in the GNOME glib commit 63c5b62f. Organizations should update to this version or later through their package management systems. The release notes are available at the GNOME glib Release 2.65.3 page.

Workarounds

• Ensure applications use static option entry lists as recommended by the vendor
• Limit the number of option entries passed to g_option_group_add_entries() to prevent overflow conditions
• Implement input validation on any user-controlled data that influences option group configurations
• Consider sandboxing or containerizing applications using vulnerable GLib versions until patching is complete

# Check GLib version on your system
pkg-config --modversion glib-2.0

# On Debian/Ubuntu systems, update GLib
sudo apt update && sudo apt upgrade libglib2.0-0

# On RHEL/CentOS/Fedora systems
sudo dnf update glib2