[UNIX] pServ Directory Traversal Vulnerability

From: SecuriTeam (support_at_securiteam.com)
Date: 01/05/04

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Date: 5 Jan 2004 16:51:51 +0200

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      pServ Directory Traversal Vulnerability
    ------------------------------------------------------------------------

    SUMMARY

    The aim of <http://sourceforge.net/projects/pserv> pServ (pico Server) is
    "to create a portable, small web server. Coded in portable C with UNIX
    being the main reference platform, but porting is encouraged. Portability
    and small footprint should enable the use of pServ on a workstation as
    well as". A directory traversal vulnerability in the product allows remote
    attackers to view files that reside outside the bound HTTP root directory.

    DETAILS

    Vulnerable systems:
     * pServ version 3.0b2

    The program, by default, has an anti-directory traversal check, but this
    check can be easily bypassed using the double slash ("//") into the HTTP
    requests.

    Exploit:
    To test the pServ's vulnerability simply send to the web server an HTTP
    request string, like that:
    GET //../ HTTP/1.0\r\n\r\n

    Or generally:
    GET //../MY_PATH HTTP/1.0\r\n\r\n
    GET /SOME_DIRECTORY//..//../ HTTP/1.0\r\n\r\n
                            
    Therefore, the web server will allow you to go outside of the
    documentsPath assigned to the web server, and navigate through the system.

    Solution:
    To fix the bug simply go on the pServ's official website,
    <http://sourceforge.net/projects/pserv>
    http://sourceforge.net/projects/pserv, and download the latest version of
    pServ (see in CVS).

    Or, if you want, you can use my following little patch, that should fix
    the bug for the version 3.0b2 of pServ:
    --- main.c 2003-09-22 10:39:24.000000000 +0200
    +++ patch.c 2003-12-19 12:40:47.000000000 +0100
    @@ -455,6 +455,11 @@
                         dirName[1] = req.documentAddress[2];
                         dirName[2] = req.documentAddress[3];
                         dirName[3] ='\0';
    + if (dirName[0] == '/')
    + {
    + sayError(sock, FORBIDDEN, req.documentAddress,
    req);
    + return -1;
    + }
                         if (!strcmp(dirName, "../"))
                         {
                             sayError(sock, FORBIDDEN, req.documentAddress,
    req); @@ -462,6 +467,15 @@
                         }
                     }
                     j = 0;
    + for(i = 1; i < sL; i++) {
    + if(req.documentAddress[i] == '/')
    + if(req.documentAddress[i+1] == '/')
    + {
    + sayError(sock, FORBIDDEN,
    req.documentAddress, req);
    + return -1;
    + }
    +
    + }
                     for (i = 1; i < sL; i++) {
                         if (req.documentAddress[i] == '/')
                         {

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:fdonato@autistici.org>
    Donato Ferrante.

    ========================================

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