[UNIX] Net::Server's log() Function Syslog Usage Allows for a Format String Vulnerability

From: SecuriTeam (support_at_securiteam.com)
Date: 04/25/05

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    Date: 25 Apr 2005 18:36:18 +0200
    
    

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      Net::Server's log() Function Syslog Usage Allows for a Format String
    Vulnerability
    ------------------------------------------------------------------------

    SUMMARY

    The undocumented but frequently used "log" function provided by the
    Net::Server Perl module is not safe against format string vulnerability.

    DETAILS

    Vulnerable Systems:
     * Net::Server version 0.87

    The syslog call in function log is implemented like following:
      ### log only to syslog if setup to do syslog
      if( $prop->{log_file} eq 'Sys::Syslog' ){
        $level = $level!~/^\d+$/ ? $level : $Net::Server::syslog_map->{$level}
    ;
        Sys::Syslog::syslog($level,@_); <---!!!!!!
        return;
      }

    Sys::Syslog tells how to use function "syslog":
           syslog $priority, $format, @args
               If $priority permits, logs ($format, @args) printed as by
               "printf(3V)", with the addition that %m is replaced with "$!"
    (the latest error message).

    Unfortunately, the function "log" of Net::Server put now the first given
    log argument into "syslog" function as format string, and the others as
    arguments.

    Workaround:
    As a workaround, programs using "log" of Net::Server can replace a single
    "%" by "%%", but only in case of when syslog is used.

    Impact of workaround: programs which call "log" of Net::Server with format
    string in first log argument will break.

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:pbieringer@aerasec.de> Dr.
    Peter Bieringer.

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