AFFLIB(TM): Multiple Buffer Overflows

2007.05.04
Risk: High
Local: No
Remote: Yes
CWE: CWE-Other


CVSS Base Score: 10/10
Impact Subscore: 10/10
Exploitability Subscore: 10/10
Exploit range: Remote
Attack complexity: Low
Authentication: No required
Confidentiality impact: Complete
Integrity impact: Complete
Availability impact: Complete

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Virtual Security Research, LLC. http://www.vsecurity.com/ Security Advisory - -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -=-=- 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 - -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -=-=- 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] = '&#65533;00'; 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()->LastModifi ed = 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/ - -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -=-=- 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 - -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -=-=- 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 - -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -=-=- 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. - -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -=-=- Vulnerability Disclosure Policy: http://www.vsecurity.com/disclosurepolicy.html - -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -=-=- 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. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQFGMjalQ1RSUNR+T+gRAuNrAJ9VCrWv8Ir/Wi5j6y6OjH9vzFPupwCfWMcS +Q3P10JutWw0NWpYNpuuIjc= =HanZ -----END PGP SIGNATURE-----


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