CERT Advisory CA-95:04.NCSA.http.daemon.for.unix.vulnerability
CERT Advisory
cert-advisory at cert.org
Fri Feb 17 22:36:01 UTC 1995
=============================================================================
CA-95:04 CERT Advisory
February 17, 1995
NCSA HTTP Daemon for UNIX Vulnerability
-----------------------------------------------------------------------------
The CERT Coordination Center has received reports that there is a
vulnerability in the NCSA HTTP Daemon V.1.3 for UNIX. Because of this
vulnerability, the daemon can be tricked into executing shell commands.
If you have any questions regarding this vulnerability, please send
e-mail to Beth Frank at the NCSA, efrank at ncsa.uiuc.edu.
-----------------------------------------------------------------------------
I. Description
A vulnerability in the NCSA HTTP Daemon allows it to be tricked into
executing shell commands.
II. Impact
Remote users may gain unauthorized access to the account (uid) under
which the httpd process is running.
III. Solution
The following solution was provided by the HTTPD Team at SDG at
NCSA.
Step 1:
In the file httpd.h, change the string length definitions
from:
/* The default string lengths */
#define MAX_STRING_LEN 256
#define HUGE_STRING_LEN 8192
to:
/* The default string lengths */
#define HUGE_STRING_LEN 8192
#define MAX_STRING_LEN HUGE_STRING_LEN
Step 2:
Install the following patch, which performs the functionality of
strsubfirst (i.e., copy src followed by dest[start] into dest) without
the use of a temporary buffer.
----------------------------------cut here-------------------------------------
*** util.c.bak Sat May 7 21:47:15 1994
--- util.c Thu Feb 16 04:17:07 1995
***************
*** 158,168 ****
void strsubfirst(int start,char *dest, char *src)
{
! char tmp[MAX_STRING_LEN];
! strcpy(tmp,&dest[start]);
! strcpy(dest,src);
! strcpy(&dest[strlen(src)],tmp);
}
/*
--- 158,174 ----
void strsubfirst(int start,char *dest, char *src)
{
! int src_len, dest_len, i;
! if ((src_len=strlen(src))<start){ /** src "fits" in dest **/
! for (i=0;dest[i]=src[i];i++);
! for (i=src_len;dest[i]=dest[i-src_len+start];i++);
! }
! else { /** src doesn't fit in dest **/
! for (dest_len=strlen(dest),i=dest_len+src_len-start;i>=src_len;i--)
! dest[i] = dest[i-src_len+start];
! for (i=0;i<src_len;i++) dest[i]=src[i];
! }
}
/*
---------------------------------cut here-------------------------------------
After you apply this patch, recompile httpd, kill the current running process,
and restart the new httpd.
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The CERT Coordination Center thanks Steve Weeber, Carlos Varela, and
Beth Frank for their support in responding to this problem.
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If you believe that your system has been compromised, contact the CERT
Coordination Center or your representative in Forum of Incident
Response and Security Teams (FIRST).
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Software Engineering Institute
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