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Path Traversal: 'C:dirname'

Draft Variant
Structure: Simple
Description

This vulnerability occurs when an application accepts user input containing Windows drive letters (like 'C:dirname') without proper validation, allowing attackers to redirect file operations to unintended locations or access arbitrary files on the system.

Extended Description

This specific path traversal variant exploits how Windows interprets file paths. When an application concatenates user-controlled input containing a drive letter (e.g., 'C:') with a base directory, it can bypass intended security boundaries. The operating system treats this as an absolute path starting from the specified drive root, potentially letting an attacker read, write, or delete sensitive files anywhere on that volume. To prevent this, developers must rigorously validate and sanitize all user input used in file system operations. Implement strict allow-lists of permitted characters, normalize paths before checking them, and ensure the final resolved path remains within the intended safe directory (e.g., using canonicalization and then checking if the path starts with the allowed base path). Never rely solely on checking for '..' sequences, as drive letter injection provides a separate bypass method.
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. 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 software 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 software.
Potential Mitigations 2
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.

Effectiveness: High

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.
Observed Examples 7
CVE-2001-0038Remote attackers can read arbitrary files by specifying the drive letter in the requested URL.
CVE-2001-0255FTP server allows remote attackers to list arbitrary directories by using the "ls" command and including the drive letter name (e.g. C:) in the requested pathname.
CVE-2001-0687FTP server allows a remote attacker to retrieve privileged system information by specifying arbitrary paths.
CVE-2001-0933FTP server allows remote attackers to list the contents of arbitrary drives via a ls command that includes the drive letter as an argument.
CVE-2002-0466Server allows remote attackers to browse arbitrary directories via a full pathname in the arguments to certain dynamic pages.
CVE-2002-1483Remote attackers can read arbitrary files via an HTTP request whose argument is a filename of the form "C:" (Drive letter), "//absolute/path", or ".." .
CVE-2004-2488FTP server read/access arbitrary files using "C:\" filenames
Applicable Platforms
Languages:
Not Language-Specific : Undetermined
Modes of Introduction
Implementation
Functional Areas
  1. File Processing
Affected Resources
  1. File or Directory
Related Weaknesses
ChildOf: Absolute Path Traversal (CWE-36)
Taxonomy Mapping
  • PLOVER
  • CERT C Secure Coding
  • Software Fault Patterns