Directory Traversal

Directory Traversal, also known as Path Traversal, is a common cybersecurity vulnerability that allows an attacker to access files and directories stored outside the intended web root folder.

It works by manipulating variables that reference files with "dot-dot-slash" sequences (../) or their encoded equivalents, which refer to parent directories.

How Directory Traversal Works

The core concept relies on how a web application handles user-supplied input when building a file path.

1. Vulnerable Code: A vulnerable application takes a filename from a user's request (e.g., a URL parameter) and uses it directly to construct a file path on the server.

   • Example (Conceptual): The server-side code might be trying to load an image or document: filePath=/var/www/images/+user_input

2. Attack Payload: An attacker replaces a standard filename with a sequence like ../. Each ../ moves one level up in the directory structure.

   • Attacker Input: ../../../etc/passwd

   • Resulting Path: If the web root is /var/www/images/, the server concatenates this to form: /var/www/images/../../../etc/passwd.

   • Server Interpretation: The server resolves this path by moving up three directories from images/ to reach the file system root (/), and then accessing the sensitive /etc/passwd file, which contains user account information on Unix-like systems.

Key Aspects and Attack Vectors

• Platform-Specific Payloads: The specific path separator depends on the operating system.

  • Linux/Unix: ../

  • Windows: $\texttt{..\}$, but often ../ works as well.

• Encoding: Attackers often use URL encoding to bypass simple input filters. For instance, ../ can be encoded as %2e%2e%2f or %2e%2e/. Double encoding (e.g., %252e%252e%252f) may also be attempted to defeat more robust filters.

• Absolute Paths: In some cases, if the application concatenates the user input with a directory path in a way that allows it to be overridden, an attacker may inject an absolute path, such as/etc/passwd, to bypass the directory traversal sequence entirely.

• Vulnerable Components: This vulnerability frequently affects components that load static files, display log files, read templates, or perform other file operations based on user input.

Impact

The impact of a successful Directory Traversal attack can be severe, leading to:

• Information Disclosure: Accessing and reading sensitive files, like:

  • Configuration files (e.g., database credentials)

  • Source code

  • System files (/etc/passwd, Windows boot.ini)

  • Logs

• Remote Code Execution (RCE): In some advanced cases, if an attacker can write to a file (a variant called Arbitrary File Write) and that file is later executed by the server (e.g., uploading a web shell to an accessible directory), RCE can be achieved.

Mitigation

The most effective way to prevent Directory Traversal attacks is to avoid passing user-supplied input directly into filesystem calls. Developers should use one or more of the following defensive measures:

1. Input Validation: Sanitize user input by rejecting any input containing directory traversal sequences (../) or their encoded variations.

2. Canonicalization and Validation: Before use user input, the application should canonicalize the path (resolve all ../ sequences to their absolute, simplest form) and then verify that the resulting path starts with the expected base directory. If it doesn't, the request should be rejected.

3. File System Access Controls: Use a "whitelist" of allowed files or file extensions, only serving files that are explicitly permitted.

4. Least Privilege: Run the web application with the lowest possible privileges to minimize the damage an attacker can do. For example, the web server user should not have read access to system-wide configuration files, such as/etc/passwd.

Directory Traversal (or Path Traversal) is a security vulnerability where an attacker manipulates variables that reference files to gain unauthorized access to files and directories outside of the intended web root folder, often $\text{use}$ing the "dot-dot-slash" sequence ($\texttt{../}$) or its encoded forms.

ThreatNG helps address this by providing an "attacker's-eye view" of your external assets, proactively identifying configurations and exposures that could lead to a successful Directory Traversal attack.

External Discovery and Continuous Monitoring

ThreatNG starts with External Discovery, performing purely external unauthenticated discovery to map and monitor your entire internet-facing attack surface. This process identifies assets and configurations where a Directory Traversal flaw would exist, such as exposed web applications, development environments, or APIs on subdomains. The platform then provides Continuous Monitoring 24/7, ensuring that newly deployed assets or configuration changes that introduce a Directory Traversal risk are detected immediately before they can be exploited.

External Assessment and Examples

ThreatNG's External Assessment capabilities directly analyze exposures that could lead to a successful Directory Traversal attack through various risk scores.

Web Application Hijack Susceptibility

This module analyzes the parts of a web application accessible from the outside world to identify potential entry points for attackers. A web page that accepts an unvalidated filename parameter is a key entry point for this attack. For example, ThreatNG might flag the discovery of a URL like [http://sub.domain.com/getFile?file=report.pdf](http://sub.domain.com/getFile?file=report.pdf) where the parameter file is not properly sanitized, allowing an attacker to inject ../../../etc/passwd to gain sensitive system file contents.

Cyber Risk Exposure

This score accounts for the discovery of specific vulnerabilities and the exposure of sensitive ports. ThreatNG identifies the Technology Stack being $\text{use}$d. Suppose a known vulnerability (a CVE) in a web server or application technology that enables Directory Traversal is discovered on an asset. In that case, that asset's Cyber Risk Exposure score will be immediately heightened. This is especially true if the vulnerability is flagged as a Known Exploited Vulnerability (KEV) by ThreatNG's intelligence.

Data Leak Susceptibility

Since Directory Traversal is a primary method for an attacker to achieve an initial data leak (e.g., retrieving configuration files or source code), ThreatNG's analysis in this area is key. It might, for instance, find a publicly exposed development environment subdomain that has an accessible Admin Page and contains multiple exposed Document Files and Txt Files on archived web pages, indicating poor file access controls that could be bypassed with a traversal attack.

Investigation Modules and Intelligence Repositories

ThreatNG provides the data and context needed to identify and prioritize Directory Traversal risks through its specialized modules and intelligence.

Investigation Modules and Examples

• Sensitive Code Exposure (Code Repository Exposure): This module directly discovers public code repositories and investigates their contents for Configuration Files or Database Exposures. Directory Traversal is often $\text{use}$d to steal these exact files from a live server. Discovering a public repository containing a config/database.yml file, for example, provides an attacker with valuable context and targets for a traversal attack on the live environment.

• Subdomain Intelligence: This involves analyzing HTTP Responses and Header Analysis on subdomains. The module identifies Admin Pages and Development Environments, which are frequent targets for attacks. For example, placing a dev.company.com subdomain with exposed Development Environments that accept file requests is a prime candidate that an attacker would test for traversal attacks.

• Search Engine Exploitation (Website Control Files): This module tracks the exposure of files, such as robots.txt. While not a security flaw itself, an attacker can use this to find excluded directories (like /files/old_reports/) and then try to escape from these directories $\text{use}$ing ../ sequences, which ThreatNG’s reporting would highlight as a possible attack vector.

Intelligence Repositories (DarCache)

ThreatNG’s DarCache Vulnerability repository provides crucial context on the exploitability of discovered risks. If a component on the organization's attack surface has a Known Exploited Vulnerability (KEV) related to Path Traversal, ThreatNG prioritizes it. Furthermore, the DarCache eXploit repository provides verified Proof-of-Concept (PoC) Exploits for specific vulnerabilities, allowing security teams to understand exactly how an attacker would use a Directory Traversal flaw against an identified asset.

Reporting and Complementary Solutions

Reporting

ThreatNG provides Prioritized Reporting that flags a confirmed Directory Traversal vulnerability on a core web asset as likely High risk, demanding immediate attention. The reports are supported by a Knowledgebase that offers specific Recommendations, such as advising developers to canonicalize and validate all user input before it is $\text{use}$d in filesystem operations. Additionally, the External GRC Assessment maps these exposures to compliance frameworks (like PCI DSS, HIPAA, GDPR, and POPIA), highlighting the regulatory impact of exposing sensitive data via traversal.

Complementary Solutions

ThreatNG’s external context is highly valuable when $\text{use}$d alongside other security tools, allowing them to focus their internal efforts.

• Security Information and Event Management (SIEM): ThreatNG provides external context to the SIEM’s internal log data. For instance, if ThreatNG detects a high-risk web application, the SIEM can be configured to aggressively alert on any unusual file access or HTTP error activity from that specific application’s logs, especially patterns indicative of Directory Traversal attempts.

• Web Application Firewall (WAF): ThreatNG identifies the exact vulnerable assets and provides specific attack context, which can be $\text{use}$d to fine-tune WAF rules. Suppose ThreatNG identifies a specific technology with a known traversal vulnerability. In that case, the information is pushed to the WAF to create a custom, high-confidence rule that blocks../ sequences only for that technology's URL path, making the WAF more effective.

• Vulnerability Management (VM) Platform: ThreatNG enriches the VM's internal scan results with real-world external exploitability context from DarCache. ThreatNG's data can instantly elevate a VM scan finding a medium-severity flaw if it confirms a linked KEV that demonstrates a Directory Traversal attack chain, ensuring immediate remediation priority within the VM platform.