CVE-2023-51714: Qt HTTP2 Buffer Overflow Vulnerability

CVE-2023-51714 Overview

CVE-2023-51714 is an integer overflow vulnerability discovered in the HTTP2 implementation of the Qt framework. The flaw exists in the HPack (Header Compression for HTTP/2) table implementation, specifically within network/access/http2/hpacktable.cpp, where an incorrect integer overflow check can be exploited. This vulnerability affects Qt versions before 5.15.17, 6.x before 6.2.11, 6.3.x through 6.5.x before 6.5.4, and 6.6.x before 6.6.2.

Critical Impact

This integer overflow vulnerability in Qt's HTTP2 HPack implementation could allow remote attackers to compromise application security with network-based attacks requiring no authentication or user interaction.

Affected Products

• Qt versions before 5.15.17
• Qt versions 6.x before 6.2.11
• Qt versions 6.3.x through 6.5.x before 6.5.4
• Qt versions 6.6.x before 6.6.2
• Debian Linux 10.0

Discovery Timeline

• 2023-12-24 - CVE-2023-51714 published to NVD
• 2025-03-20 - Last updated in NVD database

Technical Details for CVE-2023-51714

Vulnerability Analysis

This vulnerability is classified as CWE-190 (Integer Overflow or Wraparound). The flaw resides in the HPack table implementation within Qt's HTTP2 networking module. HPack is the header compression algorithm used by HTTP/2 to reduce overhead and improve performance. The integer overflow occurs due to an incorrect bounds check when processing HPack integer values, which could lead to memory corruption or other undefined behavior.

When processing HTTP2 headers, the HPack decoder must parse variable-length integers. The vulnerable code in hpacktable.cpp contains an insufficient overflow check that fails to properly validate integer values before arithmetic operations. An attacker could craft malicious HTTP2 headers that trigger this overflow condition.

Root Cause

The root cause is an incorrect integer overflow check in the HPack table implementation. Integer overflow vulnerabilities occur when arithmetic operations produce results that exceed the maximum value a data type can hold, causing the value to wrap around. In this case, the overflow check logic was flawed, allowing specially crafted input to bypass the intended safeguards and trigger undefined behavior in the application.

Attack Vector

The attack vector is network-based, meaning an attacker can exploit this vulnerability remotely without requiring any privileges or user interaction. An attacker could exploit this vulnerability by:

1. Setting up a malicious HTTP2 server that responds with crafted headers containing values designed to trigger the integer overflow
2. Crafting HTTP2 requests to vulnerable Qt-based applications that process the malicious response
3. Exploiting applications using Qt's HTTP2 client implementation that connect to attacker-controlled servers

The vulnerability manifests during HPack integer decoding within the HTTP2 header decompression process. For technical implementation details, refer to the Qt Project Code Review for the security patches.

Detection Methods for CVE-2023-51714

Indicators of Compromise

• Unusual HTTP2 traffic patterns with abnormally large or malformed header values
• Application crashes or unexpected terminations in Qt-based applications when processing HTTP2 connections
• Memory corruption signatures in application logs or crash dumps related to HPack processing

Detection Strategies

• Monitor Qt-based applications for unusual HTTP2 header processing behavior or crashes
• Implement network traffic analysis to detect anomalous HTTP2 HEADERS frames with potentially malicious HPack-encoded integers
• Deploy application-level monitoring for Qt framework version identification to track unpatched instances
• Use memory corruption detection tools during development and testing of Qt applications

Monitoring Recommendations

• Enable detailed logging for HTTP2 connections in Qt-based applications
• Implement crash reporting mechanisms to capture stack traces indicating HPack-related failures
• Monitor network boundaries for HTTP2 traffic anomalies targeting internal Qt-based services
• Regularly audit deployed Qt versions across the organization's software inventory

How to Mitigate CVE-2023-51714

Immediate Actions Required

• Upgrade Qt to a patched version: 5.15.17 or later, 6.2.11 or later, 6.5.4 or later, or 6.6.2 or later
• Audit all applications using Qt framework for HTTP2 functionality
• Apply operating system vendor patches (e.g., Debian security updates)
• Consider disabling HTTP2 support in Qt applications if immediate patching is not possible

Patch Information

Qt has released security patches to address this vulnerability. The fixes are available through the official Qt Project code review system:

• Qt Project Code Review - Patch 524864
• Qt Project Code Review - Patch 524865

For Debian-based systems, refer to the Debian LTS Announcement for distribution-specific updates.

Workarounds

• Disable HTTP2 protocol support in Qt applications by configuring HTTP/1.1 fallback where feasible
• Implement network-level filtering to inspect and block malformed HTTP2 traffic
• Use application firewalls or reverse proxies that can validate HTTP2 headers before forwarding to Qt-based backends
• Isolate Qt-based applications handling untrusted network input in sandboxed environments

# Example: Check Qt version in installed applications
qmake --version
# Example: Query package version on Debian systems
dpkg -l | grep -i qt5
apt-cache policy qtbase5-dev