CVE-2021-39929 Overview
CVE-2021-39929 is an Uncontrolled Recursion vulnerability affecting the Bluetooth DHT dissector in Wireshark versions 3.4.0 to 3.4.9 and 3.2.0 to 3.2.17. This vulnerability allows attackers to cause a denial of service condition through packet injection or by using a crafted capture file. When exploited, the recursive function calls in the Bluetooth DHT dissector can exhaust stack resources, causing Wireshark to crash and become unresponsive.
Critical Impact
Attackers can remotely crash Wireshark installations by sending malicious packets or tricking users into opening crafted capture files, disrupting network analysis operations and security monitoring capabilities.
Affected Products
- Wireshark versions 3.4.0 to 3.4.9
- Wireshark versions 3.2.0 to 3.2.17
- Fedora 34 and 35 (with vulnerable Wireshark packages)
- Debian Linux 9.0, 10.0, and 11.0 (with vulnerable Wireshark packages)
Discovery Timeline
- 2021-11-19 - CVE-2021-39929 published to NVD
- 2024-11-21 - Last updated in NVD database
Technical Details for CVE-2021-39929
Vulnerability Analysis
This vulnerability stems from improper handling of recursive operations within the Bluetooth DHT (Distributed Hash Table) dissector component of Wireshark. The dissector is responsible for parsing and analyzing Bluetooth DHT protocol traffic captured during network analysis sessions. When processing specially crafted packets or capture files, the dissector enters an uncontrolled recursive state that continues until system resources are exhausted.
The vulnerability is classified under CWE-674 (Uncontrolled Recursion), which describes situations where a function calls itself without properly limiting the recursion depth. In this case, the Bluetooth DHT dissector fails to implement adequate safeguards against deeply nested or circular data structures that trigger excessive recursive calls.
Root Cause
The root cause of CVE-2021-39929 lies in the Bluetooth DHT dissector's failure to implement proper recursion depth limits when parsing protocol data. When encountering malformed or specially crafted Bluetooth DHT packets, the dissector's parsing logic enters a recursive loop without appropriate termination conditions. This design flaw allows attackers to construct payloads that trigger unbounded recursion, ultimately leading to stack exhaustion and application crash.
Attack Vector
The attack can be executed through two primary vectors:
Packet Injection: An attacker on the same network segment can inject malicious Bluetooth DHT packets that, when captured and analyzed by Wireshark, trigger the uncontrolled recursion.
Crafted Capture File: An attacker can distribute a malicious pcap/pcapng capture file containing the crafted packets. When a user opens this file in Wireshark for analysis, the vulnerability is triggered.
The network-based attack vector requires no authentication or user interaction beyond normal network traffic capture operations. The crafted file vector requires social engineering to convince users to open the malicious file.
Detection Methods for CVE-2021-39929
Indicators of Compromise
- Unexpected Wireshark crashes during Bluetooth DHT traffic analysis
- High CPU usage followed by application termination when processing specific capture files
- Stack overflow error messages in system logs correlating with Wireshark execution
- Anomalous Bluetooth DHT protocol traffic patterns on monitored network segments
Detection Strategies
- Monitor for Wireshark process crashes and correlate with network capture activities
- Implement file integrity monitoring on capture files before analysis
- Deploy endpoint detection solutions that identify recursive crash patterns
- Analyze system logs for repeated Wireshark termination events
Monitoring Recommendations
- Enable crash reporting and logging for Wireshark installations
- Monitor network traffic for unusual Bluetooth DHT packet structures
- Track Wireshark version inventory across the organization to identify vulnerable installations
- Implement alerting for rapid succession of Wireshark process restarts
How to Mitigate CVE-2021-39929
Immediate Actions Required
- Upgrade Wireshark to version 3.4.10 or later (for 3.4.x branch) or version 3.2.18 or later (for 3.2.x branch)
- Avoid opening untrusted capture files until patched
- Consider disabling the Bluetooth DHT dissector if not required for analysis operations
- Apply operating system-level security updates from Fedora, Debian, or other distributions
Patch Information
Wireshark has released patched versions addressing this vulnerability. Users should upgrade to Wireshark 3.4.10 or later, or 3.2.18 or later, depending on their installed version branch. Additional security advisories and patch information are available through the Wireshark Security Advisory and the Wireshark Issue Tracker.
Distribution-specific updates are available:
- Debian users should consult the Debian Security Advisory DSA-5019
- Fedora users should apply updates per the Fedora Package Announcements
- Gentoo users should reference the Gentoo GLSA Advisory
Workarounds
- Disable the Bluetooth DHT dissector via Wireshark preferences: Analyze > Enabled Protocols and uncheck BT-DHT
- Avoid capturing or analyzing Bluetooth DHT traffic from untrusted sources
- Use network segmentation to limit exposure to potentially malicious Bluetooth traffic
- Implement strict file handling policies for pcap files from external sources
# Disable Bluetooth DHT dissector via command line
# Run Wireshark with the dissector disabled using the -d option
wireshark -o "bt-dht.enabled:FALSE"
# Alternative: Edit the Wireshark preferences file
# Add or modify the following line in ~/.config/wireshark/preferences
# bt-dht.enabled: FALSE
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
