Improper Handling of Apple HFS+ Alternate Data Stream Path

The software does not properly handle special paths that may identify the data or resource fork of a file on the HFS+ file system.


If the software chooses actions to take based on the file name, then if an attacker provides the data or resource fork, the software may take unexpected actions. Further, if the software intends to restrict access to a file, then an attacker might still be able to bypass intended access restrictions by requesting the data or resource fork for that file.


The Apple HFS+ file system permits files to have multiple data input streams, accessible through special paths. The Mac OS X operating system provides a way to access the different data input streams through special paths and as an extended attribute:

Resource fork: file/..namedfork/rsrc, file/rsrc (deprecated),

Data fork: file/..namedfork/data (only versions prior to Mac OS X v10.5)

Additionally, on filesystems that lack native support for multiple streams, the resource fork and file metadata may be stored in a file with "._" prepended to the name.

Forks can also be accessed through non-portable APIs.

Forks inherit the file system access controls of the file they belong to.

Programs need to control access to these paths, if the processing of a file system object is dependent on the structure of its path.


The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

A web server that interprets FILE.cgi as processing instructions could disclose the source code for FILE.cgi by requesting FILE.cgi/..namedfork/data. This might occur because the web server invokes the default handler which may return the contents of the file.

See Also

SFP Secondary Cluster: Path Traversal

This category identifies Software Fault Patterns (SFPs) within the Path Traversal cluster (SFP16).

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Weaknesses without Software Fault Patterns

CWE identifiers in this view are weaknesses that do not have associated Software Fault Patterns (SFPs), as covered by the CWE-888 view. As such, they represent gaps in...

Weaknesses Introduced During Implementation

This view (slice) lists weaknesses that can be introduced during implementation.

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