Relative Path Traversal
Draft Base
Structure: Simple
Description
This vulnerability occurs when an application builds file paths using user-supplied input without properly validating or sanitizing it. Attackers can exploit this by inserting special directory traversal sequences like '..' to access files and directories outside the intended restricted folder.
Path traversal, often called directory traversal, is a critical security flaw where an attacker manipulates file path inputs to break out of the application's intended directory. By using sequences like '../' (or its encoded equivalents), they can navigate to sensitive system files, configuration files, source code, or other restricted data. This typically happens when file operations—such as reading, writing, or deleting—rely on unsanitized user input from URLs, form fields, or cookies to construct the final path. To prevent this, developers must implement strict validation using allowlists of permitted files or directories, rather than trying to block malicious patterns. All user input used in file system operations should be canonicalized and then checked against a base directory path to ensure the final resolved path stays within the intended safe location. Server configuration should also enforce proper permissions, limiting the application's access to only necessary directories.
Common Consequences 4
Scope: IntegrityConfidentialityAvailability
Impact: Execute Unauthorized Code or Commands
The attacker may be able to create or overwrite critical files that are used to execute code, such as programs or libraries.
Scope: Integrity
Impact: Modify Files or Directories
The attacker may be able to overwrite or create critical files, such as programs, libraries, or important data. If the targeted file is used for a security mechanism, then the attacker may be able to bypass that mechanism. For example, appending a new account at the end of a password file may allow an attacker to bypass authentication.
Scope: Confidentiality
Impact: Read Files or Directories
The attacker may be able read the contents of unexpected files and expose sensitive data by traversing the file system to access files or directories that are outside of the restricted directory. If the targeted file is used for a security mechanism, then the attacker may be able to bypass that mechanism. For example, by reading a password file, the attacker could conduct brute force password guessing attacks in order to break into an account on the system.
Scope: Availability
Impact: DoS: Crash, Exit, or Restart
The attacker may be able to overwrite, delete, or corrupt unexpected critical files such as programs, libraries, or important data. This may prevent the product from working at all and in the case of a protection mechanisms such as authentication, it has the potential to lockout every user of the product.
Detection Methods 1
Automated Static AnalysisHigh
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)Potential Mitigations 3
Phase: Implementation
Strategy: Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."
Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
When validating filenames, use stringent allowlists that limit the character set to be used. If feasible, only allow a single "." character in the filename to avoid weaknesses such as Relative Path Traversal, and exclude directory separators such as "/" to avoid Absolute Path Traversal. Use a list of allowable file extensions, which will help to avoid Unrestricted Upload of File with Dangerous Type.
Do not rely exclusively on a filtering mechanism that removes potentially dangerous characters. This is equivalent to a denylist, which may be incomplete (Incomplete List of Disallowed Inputs). For example, filtering "/" is insufficient protection if the filesystem also supports the use of "\" as a directory separator. Another possible error could occur when the filtering is applied in a way that still produces dangerous data (Collapse of Data into Unsafe Value). For example, if "../" sequences are removed from the ".../...//" string in a sequential fashion, two instances of "../" would be removed from the original string, but the remaining characters would still form the "../" string.
Phase: Implementation
Strategy: Input Validation
Inputs should be decoded and canonicalized to the application's current internal representation before being validated (Incorrect Behavior Order: Validate Before Canonicalize). Make sure that the application does not decode the same input twice (Double Decoding of the Same Data). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
Use a built-in path canonicalization function (such as realpath() in C) that produces the canonical version of the pathname, which effectively removes ".." sequences and symbolic links (Relative Path Traversal, Improper Link Resolution Before File Access ('Link Following')). This includes:
- realpath() in C
- getCanonicalPath() in Java
- GetFullPath() in ASP.NET
- realpath() or abs_path() in Perl
- realpath() in PHP
Phase: Operation
Strategy: Firewall
Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].
Effectiveness: Moderate
Demonstrative Examples 3
The following URLs are vulnerable to this attack:
Code Example:
Bad
Other
otherA simple way to execute this attack is like this:
Code Example:
Attack
Other
otherID : DX-27
The following code could be for a social networking application in which each user's profile information is stored in a separate file. All files are stored in a single directory.Code Example:
Bad
Perl
perlWhile the programmer intends to access files such as "/users/cwe/profiles/alice" or "/users/cwe/profiles/bob", there is no verification of the incoming user parameter. An attacker could provide a string such as:
Code Example:
Attack
bashThe program would generate a profile pathname like this:
Code Example:
Result
bashWhen the file is opened, the operating system resolves the "../" during path canonicalization and actually accesses this file:
Code Example:
Result
bashAs a result, the attacker could read the entire text of the password file.
Notice how this code also contains an error message information leak (Generation of Error Message Containing Sensitive Information) if the user parameter does not produce a file that exists: the full pathname is provided. Because of the lack of output encoding of the file that is retrieved, there might also be a cross-site scripting problem (Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) if profile contains any HTML, but other code would need to be examined.
ID : DX-22
The following code demonstrates the unrestricted upload of a file with a Java servlet and a path traversal vulnerability. The action attribute of an HTML form is sending the upload file request to the Java servlet.Code Example:
Good
HTML
htmlWhen submitted the Java servlet's doPost method will receive the request, extract the name of the file from the Http request header, read the file contents from the request and output the file to the local upload directory.
Code Example:
Bad
Java
javaThis code does not perform a check on the type of the file being uploaded (Unrestricted Upload of File with Dangerous Type). This could allow an attacker to upload any executable file or other file with malicious code.
Additionally, the creation of the BufferedWriter object is subject to relative path traversal (Relative Path Traversal). Since the code does not check the filename that is provided in the header, an attacker can use "../" sequences to write to files outside of the intended directory. Depending on the executing environment, the attacker may be able to specify arbitrary files to write to, leading to a wide variety of consequences, from code execution, XSS (Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')), or system crash.
Observed Examples 34
CVE-2024-37032Large language model (LLM) management tool does not validate the format of a digest value (Improper Validation of Specified Type of Input) from a private, untrusted model registry, enabling relative path traversal (Relative Path Traversal), a.k.a. Probllama
CVE-2024-0520Product for managing datasets for AI model training and evaluation allows both relative (Relative Path Traversal) and absolute (Absolute Path Traversal) path traversal to overwrite files via the Content-Disposition header
CVE-2022-45918Chain: a learning management tool debugger uses external input to locate previous session logs (External Control of File Name or Path) and does not properly validate the given path (Improper Input Validation), allowing for filesystem path traversal using "../" sequences (Path Traversal: '../filedir')
CVE-2019-20916Python package manager does not correctly restrict the filename specified in a Content-Disposition header, allowing arbitrary file read using path traversal sequences such as "../"
CVE-2022-24877directory traversal in Go-based Kubernetes operator app allows accessing data from the controller's pod file system via ../ sequences in a yaml file
CVE-2020-4053a Kubernetes package manager written in Go allows malicious plugins to inject path traversal sequences into a plugin archive ("Zip slip") to copy a file outside the intended directory
CVE-2021-21972Chain: Cloud computing virtualization platform does not require authentication for upload of a tar format file (Missing Authentication for Critical Function), then uses .. path traversal sequences (Relative Path Traversal) in the file to access unexpected files, as exploited in the wild per CISA KEV.
CVE-2019-10743Go-based archive library allows extraction of files to locations outside of the target folder with "../" path traversal sequences in filenames in a zip file, aka "Zip Slip"
CVE-2002-0298Server allows remote attackers to cause a denial of service via certain HTTP GET requests containing a %2e%2e (encoded dot-dot), several "/../" sequences, or several "../" in a URI.
CVE-2002-0661"\" not in denylist for web server, allowing path traversal attacks when the server is run in Windows and other OSes.
CVE-2002-0946Arbitrary files may be read files via ..\ (dot dot) sequences in an HTTP request.
CVE-2002-1042Directory traversal vulnerability in search engine for web server allows remote attackers to read arbitrary files via "..\" sequences in queries.
CVE-2002-1209Directory traversal vulnerability in FTP server allows remote attackers to read arbitrary files via "..\" sequences in a GET request.
CVE-2002-1178Directory traversal vulnerability in servlet allows remote attackers to execute arbitrary commands via "..\" sequences in an HTTP request.
CVE-2002-1987Protection mechanism checks for "/.." but doesn't account for Windows-specific "\.." allowing read of arbitrary files.
CVE-2005-2142Directory traversal vulnerability in FTP server allows remote authenticated attackers to list arbitrary directories via a "\.." sequence in an LS command.
CVE-2002-0160The administration function in Access Control Server allows remote attackers to read HTML, Java class, and image files outside the web root via a "..\.." sequence in the URL to port 2002.
CVE-2001-0467"\..." in web server
CVE-2001-0963"..." in cd command in FTP server
CVE-2001-1193"..." in cd command in FTP server
CVE-2001-1131"..." in cd command in FTP server
CVE-2001-0480read of arbitrary files and directories using GET or CD with "..." in Windows-based FTP server.
CVE-2002-0288read files using "." and Unicode-encoded "/" or "\" characters in the URL.
CVE-2003-0313Directory listing of web server using "..."
CVE-2005-1658Triple dot
CVE-2000-0240read files via "/........../" in URL
CVE-2000-0773read files via "...." in web server
CVE-1999-1082read files via "......" in web server (doubled triple dot?)
CVE-2004-2121read files via "......" in web server (doubled triple dot?)
CVE-2001-0491multiple attacks using "..", "...", and "...." in different commands
CVE-2001-0615"..." or "...." in chat server
CVE-2005-2169chain: ".../...//" bypasses protection mechanism using regexp's that remove "../" resulting in collapse into an unsafe value "../" (Collapse of Data into Unsafe Value) and resultant path traversal.
CVE-2005-0202".../....///" bypasses regexp's that remove "./" and "../"
CVE-2004-1670Mail server allows remote attackers to create arbitrary directories via a ".." or rename arbitrary files via a "....//" in user supplied parameters.
References 5
The Art of Software Security Assessment
Mark Dowd, John McDonald, and Justin Schuh
Addison Wesley
2006
ID: REF-62
Zip Slip Vulnerability
Snyk
05-06-2018
ID: REF-1282
Secure by Design Alert: Eliminating Directory Traversal Vulnerabilities in Software
Cybersecurity and Infrastructure Security Agency
02-05-2024
ID: REF-1448
D3FEND: Application Layer Firewall
D3FEND
ID: REF-1481
Applicable Platforms
Languages:
Not Language-Specific : Undetermined
Technologies:
AI/ML : Undetermined
Modes of Introduction
Implementation
Related Attack Patterns
Alternate Terms
Zip Slip
"Zip slip" is an attack that uses file archives (e.g., ZIP, tar, rar, etc.) that contain filenames with path traversal sequences that cause the files to be written outside of the directory under which the archive is expected to be extracted [REF-1282]. It is most commonly used for relative path traversal (Relative Path Traversal) and link following (Improper Link Resolution Before File Access ('Link Following')).Functional Areas
- File Processing
Affected Resources
- File or Directory
Related Weaknesses
Taxonomy Mapping
- PLOVER
- Software Fault Patterns