Home page logo

bugtraq logo Bugtraq mailing list archives

Still security holes in NCSA httpd 1.3R
From: paulp () CERF NET (Paul Phillips)
Date: Tue, 11 Apr 1995 20:59:05 -0700

NCSA has been claiming at <URL:http://hoohoo.ncsa.uiuc.edu> that their
patch to httpd, which fixed the hole in strsubfirst, was sufficient
to fix the stack overflow bug discovered by Thomas Lopatic.  This is
incorrect.  There is at least one more instance of the same problem,
this one in log_reason.  NCSA has provided a performance reason not to
#define MAX_STRING_LEN to HUGE_STRING_LEN (i.e. you will enter swap
hell) and they are correct about that, but unfortunately that doesn't 
magically make the hole go away.

begin code traversal >>>
When accept is handed some data, httpd.c calls process_request in 

  213: process_request(0,stdout);

process_request allocates url[HUGE_STRING_LEN] for parsing out
the URL.  It calls getline in util.c to obtain the info from the 

  104: if(getline(l,HUGE_STRING_LEN,in,timeout))

process_request now decides what the method is, and calls the
relevant function.  Take GET for example: it calls process_get
in http_get.c with the url as an argument:

  143: process_get(in,out,m,url,args);

Let's say it's a standard document, so process_get calls send_node 
with the url as an argument (still possibly HUGE_STRING_LEN long)

  195: send_node(url,args,in,out);

Now send_node does various checks.  Let's say the file does not
exist: send_node wants to log it, here:

  122: log_reason("file does not exist",file);

where file is the passed url, still possible 8192 characters.
log_reason is in http_log.c, and quite short:

void log_reason(char *reason, char *file) {
    char t[MAX_STRING_LEN];

    sprintf(t,"httpd: access to %s failed for %s, reason: %s",

The file can be 8192 characters, but it's sprintfed into a 256 
character buffer.

end code traversal >>>

This particular traversal is just an example, log_reason is called
from several places with overlarge buffers.

I pointed this out to the httpd people at NCSA, who promised a
patch but haven't acted with much alacrity.  Frankly I am very
skeptical that any patch will fix all holes until I finish checking
out all the code.  When 1.4 is released to the public I will
examine it in depth as soon as possible.


Paul Phillips
paulp () cerf net

  By Date           By Thread  

Current thread:
  • Still security holes in NCSA httpd 1.3R Paul Phillips (Apr 12)
[ Nmap | Sec Tools | Mailing Lists | Site News | About/Contact | Advertising | Privacy ]