CVE-2021-4185 in Wireshark
Summary
by MITRE • 12/31/2021
Infinite loop in the RTMPT dissector in Wireshark 3.6.0 and 3.4.0 to 3.4.10 allows denial of service via packet injection or crafted capture file
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Analysis
by VulDB Data Team • 11/04/2025
The vulnerability identified as CVE-2021-4185 represents a critical denial of service flaw within Wireshark's RTMPT dissector component. This issue affects multiple versions of the popular network protocol analyzer, specifically Wireshark 3.4.0 through 3.4.10 and version 3.6.0, creating a significant risk for network security professionals who rely on this tool for packet analysis and troubleshooting. The RTMPT dissector is responsible for analyzing Real-Time Messaging Protocol over HTTP traffic, which is commonly used by Adobe Flash applications for real-time communication. When processing malformed or specially crafted RTMPT packets, the dissector enters an infinite loop that consumes excessive CPU resources and renders the application unresponsive.
The technical root cause of this vulnerability lies in insufficient input validation within the RTMPT protocol dissector implementation. When Wireshark encounters RTMPT packets that contain malformed structures or unexpected data sequences, the parsing logic fails to properly handle the edge cases that lead to infinite loop conditions. This flaw is classified as a CWE-835: Loop with Unreachable Exit Condition (Loop Iterator Not Updated) and represents a classic example of a denial of service vulnerability that can be exploited through both network packet injection and crafted capture file manipulation. The vulnerability demonstrates poor defensive programming practices where the dissector does not implement proper bounds checking or exit condition validation during packet parsing operations.
The operational impact of this vulnerability extends beyond simple application crashes, as it can be leveraged by malicious actors to perform persistent denial of service attacks against systems running Wireshark. Network security analysts and forensic investigators who use Wireshark for network monitoring, incident response, or security auditing may find their analysis tools rendered unusable by a single malicious packet or capture file. This affects the broader cybersecurity ecosystem since Wireshark is widely used across organizations for network troubleshooting, protocol analysis, and security research. The vulnerability can be exploited through various attack vectors including network packet injection, where an attacker sends malformed RTMPT packets to a target system running Wireshark, or by distributing malicious capture files that trigger the infinite loop when opened within Wireshark's interface. The attack surface is particularly concerning given that Wireshark is often used in security operations centers and forensic environments where continuous monitoring is essential.
Mitigation strategies for this vulnerability require immediate patching of affected Wireshark installations to versions that contain the necessary fixes for the RTMPT dissector. Organizations should prioritize updating their Wireshark deployments to the latest stable releases that address this specific infinite loop condition. System administrators and security teams should also implement network segmentation and monitoring to detect and prevent potential exploitation attempts. Additional defensive measures include implementing network access controls to limit exposure to potentially malicious traffic, using network intrusion detection systems to identify suspicious RTMPT traffic patterns, and establishing secure capture file handling procedures that validate file integrity before opening. The vulnerability highlights the importance of input validation and defensive programming practices in network security tools, as demonstrated by ATT&CK technique T1499.1 which covers network denial of service attacks. Security professionals should also consider implementing automated patch management systems to ensure timely remediation of similar vulnerabilities across their network infrastructure.