Vulnerability Note VU#210409

In a typical file transfer operation, one participant (the client) requests a file while a second participant (the server) provides the requested file. Before processing each request, many server implementations will consult an access control policy to determine whether the client should be permitted to read, write, or create a file at the requested location. If the client is able to craft a request that violates the server's access control policy, then the server contains a vulnerability. Since most vulnerabilities of this type involve escaping a restricted set of directories, they are commonly known as "directory traversal" vulnerabilities.

Directory traversal vulnerabilities are most often reported in server implementations, but recent research into the behavior of FTP clients has revealed several vulnerabilities in various FTP client implementations. To exploit these vulnerabilities, an attacker must convince the FTP client user to access a specific FTP server containing files with crafted filenames. When an affected FTP client attempts to download one of these files, the crafted filename causes the client to write the downloaded files to the location specified by the filename, not by the victim user. In some cases, the attacker must use a modified FTP server to allow the crafted filenames to be passed to the client.

For more detailed information regarding this research, please read "Directory Traversal Vulnerabilities in FTP Clients", written by Steve Christey.

This vulnerability allows an attacker to mislead users of affected FTP clients, convincing the victim to unintentionally create or overwrite files on the client's filesystem.

Apply a patch from your vendor

For vendor-specific information regarding vulnerability status and patch availability, please consult the Systems Affected section of this document