CVE-2021-45848 in Nicotine+
Summary
by MITRE • 03/15/2022
Denial of service (DoS) vulnerability in Nicotine+ 3.0.3 and later allows a user with a modified Soulseek client to crash Nicotine+ by sending a file download request with a file path containing a null character.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 03/24/2026
The vulnerability identified as CVE-2021-45848 represents a critical denial of service weakness within the Nicotine+ file sharing application ecosystem. This flaw affects versions 3.0.3 and later, creating a scenario where malicious actors can exploit the application's handling of file paths to cause system instability. The vulnerability specifically manifests when a modified Soulseek client sends a file download request containing a null character within the file path, leading to unexpected application behavior and potential crashes. This type of vulnerability falls under the category of improper input validation, which is commonly classified as CWE-20 - Improper Input Validation within the Common Weakness Enumeration framework.
The technical implementation of this vulnerability stems from the application's insufficient sanitization of file path data received from network connections. When Nicotine+ processes a file download request containing a null character within the file path, the application fails to properly handle this unexpected input sequence, resulting in a crash or complete application termination. The null character, represented as \x00 in hexadecimal notation, serves as a string terminator in many programming languages and operating systems, making it particularly dangerous when improperly handled in file path parsing routines. This weakness creates a direct pathway for remote attackers to disrupt service availability without requiring authentication or elevated privileges, making it particularly concerning for peer-to-peer file sharing networks where multiple users interact continuously.
The operational impact of CVE-2021-45848 extends beyond simple application crashes to potentially compromise the entire file sharing environment. When exploited successfully, this vulnerability can cause Nicotine+ clients to become unresponsive, forcing users to manually restart the application and potentially interrupting active file transfers. The attack vector is particularly insidious because it requires minimal privileges from the attacker, who only needs to establish a connection to the target system and send a specifically crafted file request. This makes the vulnerability attractive to threat actors seeking to disrupt file sharing services or create chaos within peer-to-peer networks. From an ATT&CK framework perspective, this vulnerability aligns with T1499.004 - Endpoint Denial of Service, specifically targeting the availability aspect of the system's operational capabilities.
Mitigation strategies for this vulnerability should focus on implementing robust input validation mechanisms within the Nicotine+ application. The most effective approach involves sanitizing all file path data received through network connections, ensuring that null characters are either removed or properly escaped before processing. Additionally, implementing proper error handling and graceful degradation techniques can help prevent complete application crashes when malformed input is encountered. System administrators should consider updating to patched versions of Nicotine+ as soon as available, while network monitoring solutions can be configured to detect unusual file transfer patterns that might indicate exploitation attempts. The vulnerability also highlights the importance of secure coding practices, particularly around input validation and string handling, which should be reinforced through proper security training for developers working on networked applications. Organizations using Nicotine+ in enterprise environments should consider implementing network segmentation and access controls to limit potential attack surfaces and reduce the impact of such vulnerabilities.