Path Traversal: '/absolute/pathname/here'

Description

This vulnerability occurs when an application accepts user input containing absolute file paths (starting with a forward slash like '/etc/passwd') and uses it to access files without proper security checks. Attackers can exploit this to read, write, or delete sensitive files anywhere on the server's filesystem.

Extended Description

Path traversal vulnerabilities using absolute paths are dangerous because they give attackers direct navigation to any location the application can reach. Unlike relative paths ('../'), absolute paths like '/home/user/config.ini' or '/var/log/app.log' point to specific system locations, bypassing intended directory restrictions entirely. This often happens when file operations use unsanitized user input—such as from URL parameters, form fields, or API requests—to construct filesystem paths. To prevent this, developers should avoid using user-supplied input for file operations whenever possible. If file access based on input is required, implement strict allow-listing of permitted paths, normalize and validate inputs against a known safe directory, and run the application with minimal filesystem permissions. Using security mechanisms like chroot jails or sandboxing can also limit the potential damage of a successful attack.

Common Consequences 1

Scope: ConfidentialityIntegrity

Impact: Read Files or DirectoriesModify Files or Directories

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 6

CVE-2002-1345Multiple FTP clients write arbitrary files via absolute paths in server responses

CVE-2001-1269ZIP file extractor allows full path

CVE-2002-1818Path traversal using absolute pathname

CVE-2002-1913Path traversal using absolute pathname

CVE-2005-2147Path traversal using absolute pathname

CVE-2000-0614Arbitrary files may be overwritten via compressed attachments that specify absolute path names for the decompressed output.

Applicable Platforms

Languages:

Not Language-Specific : Undetermined

Modes of Introduction

Implementation

Functional Areas

File Processing

Affected Resources

File or Directory

Related Weaknesses

ChildOf:

Absolute Path Traversal (CWE-36)

ChildOf:

Improper Neutralization of Leading Special Elements (CWE-160)

Taxonomy Mapping

PLOVER
CERT C Secure Coding
Software Fault Patterns