CVE-2021-43970 in Quicklert
Summary
by MITRE • 03/10/2022
An arbitrary file upload vulnerability exists in albumimages.jsp in Quicklert for Digium 10.0.0 (1043) via a .mp3;.jsp filename for a file that begins with audio data bytes. It allows an authenticated (low privileged) attacker to execute remote code on the target server within the context of application's permissions (SYSTEM).
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Analysis
by VulDB Data Team • 03/12/2022
The vulnerability CVE-2021-43970 represents a critical arbitrary file upload flaw in Quicklert for Digium version 10.0.0, specifically within the albumimages.jsp component. This issue arises from insufficient input validation and file extension filtering mechanisms that fail to properly sanitize user-supplied filenames. The vulnerability is particularly concerning because it allows authenticated attackers with low privilege levels to escalate their access and execute arbitrary code on the target server. The attack vector involves uploading a specially crafted file with a filename that combines a legitimate audio extension .mp3 with a server-side include extension .jsp, creating a hybrid filename that bypasses standard security checks.
The technical exploitation of this vulnerability leverages a classic file upload security flaw where the application fails to properly validate the file content and extension combination. When an attacker uploads a file named something like "malicious.mp3;.jsp", the server may accept this file due to incomplete validation logic that only checks the file extension at the end of the filename rather than examining the entire filename structure. This allows the malicious .jsp file to be stored on the server and subsequently executed as a web shell or code execution payload. The vulnerability falls under CWE-434 which specifically addresses unrestricted file upload vulnerabilities, where the application accepts potentially malicious files without proper validation. This weakness enables attackers to bypass traditional security controls and gain unauthorized access to the server's file system and execution environment.
The operational impact of CVE-2021-43970 is severe and far-reaching for organizations using Quicklert for Digium. An authenticated attacker can leverage this vulnerability to execute code with the same privileges as the application itself, potentially leading to complete system compromise. The vulnerability allows for persistent backdoor access, data exfiltration, and further lateral movement within the network. This attack scenario aligns with ATT&CK technique T1190 which covers exploitation of vulnerabilities in applications, and T1059 which covers command and scripting interpreter usage. The low privilege requirement makes this vulnerability particularly dangerous as it can be exploited by users with minimal access rights, potentially allowing attackers to establish persistent access points and escalate privileges over time.
Organizations should implement immediate mitigations including strict file type validation, proper filename sanitization, and content-based file verification. The most effective approach involves rejecting files with multiple extensions or special characters in filenames, implementing robust file type detection based on magic numbers rather than extensions alone, and ensuring that uploaded files are stored in non-executable directories. Additionally, network segmentation and monitoring should be enhanced to detect suspicious file upload activities. The vulnerability demonstrates the importance of defense-in-depth strategies and proper input validation practices that align with security frameworks such as OWASP Top Ten and NIST Cybersecurity Framework. Regular security assessments and patch management processes should be strengthened to prevent similar vulnerabilities from being introduced into web applications and to ensure that all authentication and authorization controls are properly enforced.