AFFLIB(TM): Multiple Buffer Overflows
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Virtual Security Research, LLC.
http://www.vsecurity.com/
Security Advisory
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Advisory Name: Multiple Buffer Overflows Discovered in AFFLIB
Release Date: 2007-04-27
Application: AFFLIB(TM)
Versions: 2.2.0 and likely earlier
Severity: High
Author: Timothy D. Morgan <tmorgan {at} vsecurity {dot} com>
Vendor Status: Vendor Notified, Fix Available
CVE Candidate: CVE-2007-2053
Reference:
http://www.vsecurity.com/bulletins/advisories/2007/afflib-overflows.txt
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Product Description:
> From the forensicswiki.org website[1]:
"The Advanced Forensics Format (AFF) is an extensible open format for
the storage of disk images and related forensic metadata. It was
developed by Simson Garfinkel and Basis Technology."
AFFLIB(TM) is the reference implementation of the AFF(TM) format,
written primarily by Simson Garfinkel. It comes in the form of an open
source library and a set of command line tools used to manipulate
AFF(TM) files.
Vulnerability Overview:
In mid-March, 2007 Virtual Security Research, LLC (VSR) performed a
security code review of AFFLIB(TM) as a part of an internal tool
assessment process. As a result, multiple vulnerabilities of varying
severities were discovered. The most significant of these
vulnerabilities are being announced publicly to raise awareness and help
end-users secure themselves against potential attack.
Multiple buffer overflows were found in AFFLIB(TM) which could allow an
attacker to create a denial-of-service condition against a forensics
examiner, or possibly to execute arbitrary code on the behalf of a
victim. One such overflow may be triggered remotely and may be
relatively easy to exploit. The other overflows identified appear to
have medium to low severity, due to the low likelihood of an attacker
having the ability to influence the vulnerable operations, at least in
the typical use case scenarios. However, because AFFLIB(TM) is in part
a library, other applications may utilize it in unanticipated ways,
which may expose these attack vectors.
All identified overflows were fixed in version 2.2.6. All line numbers
listed below are from version 2.2.0.
Vulnerability Details:
The following sections include detailed descriptions of the most severe
overflows found during the assessment.
* Remote Stack-based Buffer Overflow Through Use of LastModified *
File: lib/s3.cpp
Line: 113
The LastModified string is copied to a fixed-length buffer using
strcpy(3), but no length checking is apparently done when it is
originally read from an XML response. This could allow a malicious
Amazon S3 server or a man-in-the-middle to execute code on the S3 client
system. (See [2] for more details on the Amazon S3 protocol.) Lines
111-115 illustrate the problem:
/* Make date nice */
char tstamp[64];
strcpy(tstamp,(*i)->LastModified.c_str());
tstamp[10] = ' ';
tstamp[19] = '\000';
Note that the (*i)->LastModified string is drawn directly from an XML
response in the endElement() callback function (lines 173-178 of
lib/s3_glue.cpp):
case 3:
if(!strcmp(name,"Key")){ einfo->lbr->contents.back()->Key = einfo->cbuf;
break;}
if(!strcmp(name,"LastModified")){einfo->lbr->contents.back()->LastModified =
einfo->cbuf;break;}
if(!strcmp(name,"ETag")){ einfo->lbr->contents.back()->ETag =
einfo->cbuf;break;}
if(!strcmp(name,"Size")){ einfo->lbr->contents.back()->Size =
atoi(einfo->cbuf.c_str());break;}
break;
An exploit of this would require that users decide to run the s3 binary
program against an untrustworthy S3 server, or an attacker were able to
conduct impersonation or man-in-the-middle attacks against the
communications between the user and a valid S3 server. Since the s3
binary uses non-SSL HTTP connections by default, this may not be
difficult.
* Stack-based Buffer Overflows in S3 URL Parsing *
File: lib/vnode_s3.cpp
Lines: 80 & 81
Description:
A portion of a potentially untrustworthy parameter is copied into a
buffer without sufficient length checking in a memcpy() call, which
writes to a stack-based buffer. If this function receives URLs from an
untrusted source, code execution would be a major risk. Lines 66-81 are
included below for illustration:
/* Separate out the bucket and the path */
const char *fn = af_filename(af);
regex_t re;
if(regcomp(&re,"^s3://([^/]*)/(.*)$",REG_EXTENDED)){
err(1,"regcomp");
}
regmatch_t match[3];
memset(match,0,sizeof(match));
if(regexec(&re,fn,3,match,0)!=0){
return -1; // can't parse URL; must not be a match
}
char bucket[1024]; memset(bucket,0,sizeof(bucket));
char path[1024]; memset(path,0,sizeof(path));
memcpy(bucket,fn+match[1].rm_so,match[1].rm_eo-match[1].rm_so);
memcpy(path,fn+match[2].rm_so,match[2].rm_eo-match[2].rm_so);
The overflow occurs because the length specified to memcpy() is the
length of the regular expression match, without regard to the size of
the path buffer. This may be exploitable in scenarios where an attacker
could pass command line parameters to a privileged aimage program, or
via a program written by a third-party developer.
* Stack-based Buffer Overflow in libewf Vnode Wrapper *
File: lib/vnode_ewf.cpp
Line: 70
Description:
A potentially untrustworthy parameter is used without length checking in
a strcpy() call which writes to a stack-based buffer. If this command
receives parameters from an untrusted source, code execution would be a
major risk. Lines 59-70 are included to illustrate the problem:
static int ewf_open(AFFILE *af)
{
if(strchr(af->fname,'.')==0) return -1; // need a '.' in the filename
/* See how many files there are to open */
char **files = (char **)malloc(sizeof(char *));
int nfiles = 1;
files[0] = strdup(af->fname);
char fname[MAXPATHLEN+1];
strcpy(fname,af->fname);
An overflow could occur because the af->fname string is provided by the
user, and is not limited to MAXPATHLEN. An attacker could use this in
scenarios where a 3rd-party program incorporates AFFLIB(TM) into their
program (which ultimately accepts file names from an untrusted source)
or in situations where an AFFLIB(TM) binary is setuid/setgid or is
executed remotely web applications.
* Stack-based Buffer Overflow in AFD Vnode Wrapper *
File: lib/vnode_afd.cpp
Line: 405
Description:
A potentially untrustworthy parameter is used without length checking in
a strcpy() call which writes to a stack-based buffer. If this command
receives parameters from an untrusted source, code execution would be a
major risk. Lines 402-412 are included below for illustration:
while ((dp = readdir(dirp)) != NULL){
if (last4_is_aff(dp->d_name)){
char path[MAXPATHLEN+1];
strcpy(path,af->fname);
strlcat(path,"/",sizeof(path));
strlcat(path,dp->d_name,sizeof(path));
if(afd_add_file(af,path)){
return -1;
}
}
}
The overflow would occur if a value for af->fname were specified by a
user which was larger than 1025 bytes. This is certainly plausible,
since many systems allow pathnames to be as large as 4096 bytes. As
this is part of the core AFFLIB(TM), it could be exploited in 3rd party
programs which include AFFLIB(TM) support, if an attacker were allowed
to specify filenames. In addition, it could be exploited if any
AFFLIB(TM) binary were setuid/setgid, or if these programs were executed
from a CGI script or similar remote connection.
* Stack-based Buffer Overflow in aimage Input File Name *
File: aimage/aimage.cpp
Line: 554
Description:
A command line parameter is used without length checking in a sprintf()
call, which writes to a stack-based buffer. If this command (or this
function) receives parameters from an untrusted source, code execution
would be a major risk. Lines 548-554 are included for illustration:
int getlock(class imager *im)
{
/* If the file exists and the PID in the file is running,
* can't get the lock.
*/
char lockfile[MAXPATHLEN];
sprintf(lockfile,"/tmp/aimge.%s.lock",im->infile);
An attacker could exploit this problem if the aimage binary were
setuid/setgid, or if the aimage program were executed in a CGI script or
something similar.
Vendor Response:
Simson Garfinkel was first contacted on 2007-03-31. The following
timeline outlines the responses from the vendor regarding this issue:
2007-04-01 - Vendor provided details of all vulnerabilities
identified.
2007-04-03 - Continued vendor communication.
2007-04-05 - Vendor released version 2.2.6, containing multiple
security fixes.
2007-04-06 - Vendor notified VSR that fixes were released.
2007-04-09 - VSR notified vendor that 9 vulnerability instances still
remained in latest release.
2007-04-12 - Vendor confirmed that remaining vulnerabilities would be
fixed in next release.
2007-04-25 - Vendor released versions 2.2.7 and 2.2.8. Vendor did not
notify VSR.
2007-04-27 - VSR discovered new versions were released. VSR inspected
version 2.2.8 and found that no additional vulnerabilities
were fixed. VSR advisories published.
Recommendation:
AFFLIB(TM) users should upgrade to the newest version. Third-party
projects which rely on AFFLIB(TM) should encourage users to upgrade,
and/or incorporate fixes into their distribution of the library.
The update is available via:
http://www.afflib.org/downloads/
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Common Vulnerabilities and Exposures (CVE) Information:
The Common Vulnerabilities and Exposures (CVE) project has assigned
the following name to these issues. This is a candidate for inclusion
in the CVE list (http://cve.mitre.org), which standardizes names for
security problems.
CVE-2007-2053
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References:
1. AFF - Forensics Wiki
http://www.forensicswiki.org/wiki/AFF
2. Amazon Simple Storage Service (Amazon S3).
http://www.amazon.com/gp/browse.html?node=16427261
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This advisory is distributed for educational purposes only, and comes
with absolutely NO WARRANTY; not even the implied warranty of
merchantability or fitness for a particular purpose. Virtual Security
Research, LLC nor the author accepts any liability for any direct,
indirect, or consequential loss or damage arising from use of, or
reliance on, this information.
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Vulnerability Disclosure Policy:
http://www.vsecurity.com/disclosurepolicy.html
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AFF(TM) and AFFLIB(TM) are trademarks of Simson Garfinkel and Basis
Technology Corp.
Included source code excerpts are copyright Simson Garfinkel and Basis
Technology Corp.
This advisory is copyright (C) 2007 Virtual Security Research, LLC. All
rights reserved.
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