Tutorial - http server read access

## http Server Read Access

Updated 2/9/01

### Impact

The web server allows remote users to read arbitrary files on the system. If the password or shadow file can be read, the attacker could crack account passwords and gain access to the system.

### Background

Web servers normally service requests for files under their document root directory. For example, if server has its root directory in `/var/www/htdocs`, and it receives a request for `http://server/page.html`, it sends the file `/var/www/htdocs/page.html` back to the client.

### The Problem

Operating systems allow path names to refer to a parent directory using the "`../`" string. An attacker could attempt to exploit this feature to retrieve files from directories outside of the document root directory. Most web servers remove the "`../`" strings from requested URLs. However, some web servers can still be exploited by using three dots instead of two ("`.../`") or by including backslash characters ("`\../`" or "`..\`"). Others can be tricked into accepting a "`../`" by encoding the dots into their hexadecimal ASCII representation. Thus a pathname including one or more instances of the string "`%2E%2E/`" could be used to retrieve arbitrary files from the server.

Related CVE entries:
CVE 2000-0920 BOA web server
CVE 2001-0189 LocalWEB2000
CVE 2001-0462 Perl web server
CVE 2001-0467 RobTex Viking
CVE 2001-0495 DataWizard WebXQ
CVE 2001-0574 MP3Mystic
CVE 2001-0615 Faust Informatics Freestyle chat server
CVE 2001-0982 IBM Tivoli WebSEAL Policy Director

### Resolutions

Contact the vendor of the web server for a fix. If a fix is unavailable, it would be advisable to choose a different web server.

### Where can I read more about this?

For an example of this vulnerability, see Bugtraq and CORE-SDI.