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Bug #6351 '%'-characters in syslog()-function
Submitted: 2000-08-25 08:22 UTC Modified: 2000-09-17 17:10 UTC
From: jjaakkol at cs dot helsinki dot fi Assigned:
Status: Closed Package: *General Issues
PHP Version: 4.0.1pl2 OS: Any OS with syslog()
Private report: No CVE-ID: None
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 [2000-08-25 08:22 UTC] jjaakkol at cs dot helsinki dot fi 
syslog() function has a client given format string vulneralibity (this is actually
known, since there is a comment on this in the sources).

# cat test.php
<?php
syslog(5,"%s");
?>
 
# php4 test.php
Content-type: text/html
 
 
# tail -1 /var/log/messages
Aug 25 15:05:12 demonstration php4: U??f?^HVS<u^Lf}^H^Bu^W?E?P?E?Pj^B??^^A         

However, I guess that  this could be exploited to gain access to PHP-server in scripts who syslog() some client given data. So this is a security problem too.

The simple fix is to change the line 
php_syslog((*priority)->value.lval, (*message)->value.str.val);
in ext/standard/syslog.c to
php_syslog((*priority)->value.lval,"%s", (*message)->value.str.val);

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 [2000-08-27 06:03 UTC] stas@php.net 
Seems to be a real bug. We should or require parameters for %-s, or inhibit them at all, and use %s for it. 

Contrary to what user says, I do not see a way to exploit it actively (like, for modifying any data on the server), but this can easily lead for crash, since garbage pointer is referenced.
 [2000-08-27 07:29 UTC] jjaakkol at cs dot helsinki dot fi 
This kind of "format bugs" have been exploited before.
At least wu-ftpd and proftpd have been vulnerable to format bugs. See BugTraq mailing list last july for details
(especially the thread "paper: format bugs").
I don't know for sure if this could be exploided in PHP, but my best guess is that it probably could be.

IMHO, the best fix would be to just use syslog("%s",string). You only need five more characters but no change in the
PHP-syslog function API.
 [2000-09-17 17:10 UTC] stas@php.net 
fixed in CVS.
 
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