Multiple Vendor wget/curl NTLM Username Buffer Overflow Vulnerability iDEFENSE Security Advisory 10.13.05 www.idefense.com/application/poi/display?id=322&type=vulnerabilities October 13, 2005 I. BACKGROUND GNU Wget is a free software package for retrieving files using HTTP, HTTPS and FTP, the most widely-used Internet protocols. It is a non-interactive commandline tool, so it may easily be called from scripts, cron jobs, terminals without X-Windows support, etc. More information on Wget is available from the vendor website: http://www.gnu.org/software/wget/wget.html curl is a command line tool for transferring files with URL syntax, supporting FTP, FTPS, HTTP, HTTPS, GOPHER, TELNET, DICT, FILE and LDAP. Curl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading, HTTP form based upload, proxies, cookies, user+password authentication (Basic, Digest, NTLM, Negotiate, kerberos...), file transfer resume, proxy tunneling and a busload of other useful tricks. More information on curl is available from the vendor website: http://curl.haxx.se/ II. DESCRIPTION Remote exploitation of a buffer overflow vulnerability in multiple vendor's implementations of curl and wget allows attackers to execute arbitrary code. The vulnerability specifically exists due to insufficient bounds checking on user-supplied data supplied to a memory copy operation. The memcpy() of the supplied ntlm username to ntlmbuf shown below results in a stack overflow: http-ntlm.c in ntlm_output() on line 532: /* size is now 64 */ size=64; ntlmbuf[62]=ntlmbuf[63]=0; memcpy(&ntlmbuf[size], domain, domlen); size += domlen; memcpy(&ntlmbuf[size], usr, userlen); size += userlen; The resulting stack overflow can be leveraged to gain arbitrary code execution with user privileges. III. ANALYSIS Successful exploitation of the vulnerability allows remote attackers to execute arbitrary code with permissions of the http client process. User interaction is required. Exploitation requires a user to use one of the affected clients to connect to a malicious website. This vulnerability affects both wget and curl clients similarly because wget 1.10 adopted the curl ntlm authentication source code into its own code base. The described vulnerability requires that ntlm authentication is enabled in the affected client versions. A factor that somewhat increases the risk of this vulnerability is that a client can be forced to reconnect using ntlm authentication by issuing a HTTP 302 REDIRECT command to the connecting client. IV. DETECTION iDEFENSE Labs has confirmed the following software versions are vulnerable: * wget 1.10 * curl 7.13.2 * libcurl 7.13.2 V. WORKAROUND As a workaround solution, disable NTLM support in wget and curl installations. VI. VENDOR RESPONSE wget 1.10.2 has been released to address this issue and is available for download at: http://ftp.gnu.org/pub/gnu/wget/ curl has released the following patch to address this issue: http://curl.haxx.se/libcurl-ntlmbuf.patch curl has also released the following security advisory: http://curl.haxx.se/mail/lib-2005-10/0061.html Additionally, the maintainers of curl-web have provided the following details on affected versions: Affected versions: curl and libcurl 7.10.6 to and including 7.14.1 Not affected versions: curl and libcurl 7.10.5 and earlier, 7.15.0 and later VII. CVE INFORMATION The Common Vulnerabilities and Exposures (CVE) project has assigned the name CAN-2005-3185 to this issue. This is a candidate for inclusion in the CVE list (http://cve.mitre.org), which standardizes names for security problems. VIII. DISCLOSURE TIMELINE 10/12/2005 Initial vendor notification 10/12/2005 Initial vendor response 10/13/2005 Coordinated public disclosure IX. CREDIT The discoverer of this vulnerability wishes to remain anonymous. Get paid for vulnerability research http://www.idefense.com/poi/teams/vcp.jsp Free tools, research and upcoming events http://labs.idefense.com X. LEGAL NOTICES Copyright (c) 2005 iDEFENSE, Inc. Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDEFENSE. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please email customerservice (at) idefense (dot) com [email concealed] for permission. Disclaimer: The information in the advisory is believed to be accurate at the time of publishing based on currently available information. Use of the information constitutes acceptance for use in an AS IS condition. There are no warranties with regard to this information. Neither the author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information.