CVE-2020-17507: Qt Buffer Overflow Vulnerability

CVE-2020-17507 Overview

CVE-2020-17507 is an Out-of-Bounds Read vulnerability discovered in the Qt framework affecting versions through 5.12.9 and 5.13.x through 5.15.x before 5.15.1. The vulnerability exists in the read_xbm_body function within gui/image/qxbmhandler.cpp, which is responsible for parsing XBM (X BitMap) image files. A malformed XBM image can trigger a buffer over-read condition, potentially causing application crashes or information disclosure.

Critical Impact

Applications using Qt's image handling capabilities may be vulnerable to denial of service attacks when processing maliciously crafted XBM image files. The network attack vector means this can be exploited remotely without authentication.

Affected Products

• Qt versions through 5.12.9
• Qt versions 5.13.x through 5.15.x before 5.15.1
• Debian Linux 9.0
• Fedora 31 and 32

Discovery Timeline

• August 12, 2020 - CVE-2020-17507 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-17507

Vulnerability Analysis

The vulnerability resides in the XBM image format handler within Qt's GUI module. XBM is a monochrome image format historically used in X Window System applications. The read_xbm_body function in qxbmhandler.cpp is responsible for parsing the body of XBM image data and constructing the corresponding image in memory.

The buffer over-read condition occurs when the function processes XBM image data without properly validating the boundaries of the input buffer. This is classified as CWE-125 (Out-of-bounds Read), which occurs when software reads data past the end or before the beginning of the intended buffer.

When processing a specially crafted XBM file, the vulnerable code may attempt to read memory beyond the allocated buffer boundaries. This can result in reading sensitive data from adjacent memory regions or, more commonly, causing the application to crash due to accessing invalid memory addresses.

Root Cause

The root cause of this vulnerability is insufficient boundary checking in the read_xbm_body function when parsing XBM image data. The function fails to properly validate that the image dimensions and data specified in the XBM file are consistent with the actual buffer size, allowing an attacker to craft an XBM file that causes the parser to read beyond the allocated buffer.

Attack Vector

The vulnerability is exploitable over the network without requiring any privileges or user interaction. An attacker can exploit this vulnerability by:

1. Crafting a malicious XBM image file with manipulated header values or truncated data
2. Delivering the malicious image to an application that uses Qt's image handling (e.g., via web content, email attachments, or file sharing)
3. When the Qt-based application attempts to load and parse the image, the buffer over-read is triggered

The vulnerability affects any Qt-based application that processes XBM images, including web browsers, image viewers, document viewers, and other graphical applications built with the Qt framework.

Detection Methods for CVE-2020-17507

Indicators of Compromise

• Unexpected application crashes in Qt-based applications when opening image files
• Process crashes with stack traces referencing qxbmhandler.cpp or read_xbm_body
• Memory access violations in Qt image processing components
• Core dumps showing out-of-bounds read patterns in image parsing routines

Detection Strategies

• Monitor for abnormal termination of Qt-based applications with crash signatures related to image processing
• Implement file integrity monitoring to detect unusual XBM files in user-accessible directories
• Deploy endpoint detection rules to identify malformed XBM files based on header inconsistencies
• Use memory sanitizers (AddressSanitizer, Valgrind) during development and testing to catch buffer over-reads

Monitoring Recommendations

• Enable crash reporting and analysis for Qt-based applications in production environments
• Monitor network traffic for suspicious XBM file transfers, particularly with unusual size characteristics
• Implement application-level logging for image processing operations to identify patterns of failed image loads
• Review system logs for segmentation faults or memory access violations in Qt application processes

How to Mitigate CVE-2020-17507

Immediate Actions Required

• Upgrade Qt to version 5.15.1 or later, which contains the security fix for this vulnerability
• For systems using Qt 5.12.x LTS, apply the appropriate vendor-provided security patches
• Review and update Qt packages on all affected Linux distributions (Debian, Fedora, openSUSE)
• Consider temporarily disabling XBM image format support if immediate patching is not feasible

Patch Information

Qt has released security patches addressing this vulnerability through their code review system. The fixes are available at the following locations:

• Qt Code Review Changes - Patch 308436
• Qt Code Review Changes - Patch 308495
• Qt Code Review Changes - Patch 308496

Linux distributions have also released security updates:

• Debian LTS Security Announcement
• Gentoo GLSA 202009-04
• Fedora has released package updates for Fedora 31 and 32

Workarounds

• Restrict processing of XBM image files from untrusted sources until patches can be applied
• Implement input validation to reject XBM files before they reach Qt's image parser
• Use application sandboxing to limit the impact of potential exploitation
• Configure firewalls to block or inspect XBM file transfers from external sources

# Example: Check Qt version on Linux systems
qmake --version
# Update Qt packages on Debian/Ubuntu
sudo apt update && sudo apt upgrade libqt5gui5
# Update Qt packages on Fedora
sudo dnf update qt5-qtbase