CVE-2018-8909 in Wire
Summary
by MITRE
The Wire application before 2018-03-07 for Android allows attackers to write to pathnames outside of the downloads directory via a ../ in a filename of a received file, related to AssetService.scala.
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Analysis
by VulDB Data Team • 01/16/2020
The vulnerability identified as CVE-2018-8909 affects the Wire communication application for android systems prior to version 2018-03-07. This represents a classic path traversal flaw that enables malicious actors to manipulate file system operations by exploiting improper input validation mechanisms within the application's file handling components. The vulnerability specifically resides in the AssetService.scala file which governs how files are processed and stored within the application's download directory structure. The flaw manifests when the application fails to properly sanitize user-supplied filenames that contain directory traversal sequences, allowing attackers to craft malicious file names that include the "../" pattern to navigate outside of intended storage boundaries.
The technical implementation of this vulnerability stems from inadequate path validation and sanitization within the file processing pipeline. When Wire receives files from remote sources, it processes these files through AssetService.scala which does not sufficiently validate or sanitize the filenames before storing them on the device's file system. This creates a condition where a specially crafted filename containing directory traversal sequences can cause the application to write files to arbitrary locations on the device, potentially bypassing the intended download directory restrictions. The vulnerability essentially allows an attacker to manipulate the file system path resolution mechanism through the use of relative path references that traverse up the directory tree.
From an operational perspective, this vulnerability presents significant security implications for Wire users who may unknowingly receive malicious files that could be written to sensitive system locations. Attackers could potentially write malicious executables, configuration files, or data files to critical directories within the Android file system, potentially leading to privilege escalation, persistent malware installation, or data exfiltration. The impact extends beyond simple file corruption as the vulnerability could enable attackers to overwrite system files, install backdoors, or create persistent access points within the device. This type of vulnerability particularly threatens users who frequently exchange files through the application and may not be aware of the security implications of accepting files from untrusted sources.
The vulnerability aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. This weakness allows attackers to access files and directories that are stored outside the intended directory structure, potentially leading to unauthorized information disclosure, modification, or deletion of system resources. From an attack framework perspective, this vulnerability could be leveraged as part of a broader attack chain, potentially enabling initial access or privilege escalation within the Android environment. The ATT&CK framework would categorize this as a technique involving file and directory permissions modification, potentially supporting later stages of an attack such as privilege escalation or persistence establishment.
Mitigation strategies for this vulnerability include immediate application updates to version 2018-03-07 or later, which would contain proper input validation and sanitization mechanisms. Organizations should implement network-level controls to monitor and restrict file transfers through the Wire application, particularly for sensitive environments. Additionally, users should be educated about the risks of accepting files from untrusted sources and the importance of keeping applications updated. System administrators should consider implementing file system access controls and monitoring for unauthorized file modifications in sensitive directories. The fix typically involves implementing proper input validation that strips or escapes directory traversal sequences from filenames before processing, ensuring that all file operations occur within designated safe directories. Regular security audits of file handling components and input validation mechanisms should be conducted to prevent similar vulnerabilities from emerging in the future.