From xforce@iss.net Fri Jun 18 03:22:40 1999 From: X-Force To: alert@iss.net Cc: X-Force Date: Thu, 17 Jun 1999 23:24:51 -0400 (EDT) Subject: ISSalert: ISS Vulnerability Alert: Malformed HTR File Vulnerability in Microsoft Internet Information Server 4.0 TO UNSUBSCRIBE: email "unsubscribe alert" in the body of your message to majordomo@iss.net Contact alert-owner@iss.net for help with any problems! --------------------------------------------------------------------------- -----BEGIN PGP SIGNED MESSAGE----- ISS Vulnerability Alert June 17, 1999 Malformed HTR File Vulnerability in Microsoft Internet Information Server 4.0 Synopsis Microsoft Internet Information Server (IIS) 4.0 includes the ability to remotely administer user passwords via a web browser. IIS is a popular web server application for Windows NT, and comprises the majority of Windows NT based web servers. On June 16th it was reported to several security mailing lists that excessively long requests for .HTR files will overflow an internal buffer and allow the remote execution of arbitrary code. Affected Versions Microsoft Internet Information Server (IIS) 4.0 as installed with Option Pack 4 on all Windows NT 4.0 systems through Service Pack 5 are vulnerable to this exploit. Description IIS 4.0 contains the ability to remotely administer user passwords via "HTR" files. Requests for files ending with ".HTR" are passed to an external DLL for processing. The DLL responsible for parsing HTR requests, ISM.DLL, contains unchecked buffers thatcould allow a long request to overflow these buffers and crash the IIS service. This hole has also been demonstrated to allow remote execution of arbitrary code and exploits have been made widely available. The remote password administration feature is implemented through the "/iisadmpwd/" directory in the server's document root via ".HTR" files. HTTP requests made for ".HTR" files are mapped to be redirected to an ISAPI handler DLL which will further process the request. This vulnerability is being actively exploited on the Internet due to the wide availability of exploitation code. Programs to remotely exploit this vulnerability have been made available for both Unix and Windows environments. In addition to these programs, preliminary information shows that worms that actively exploit this hole and seek out other vulnerable hosts have been or are currently being developed. The development of these programs before a patch was available from Microsoft was expedited by the decision of the vulnerability discoverers to release exploitation code. Recommendations If your computers or websites run IIS 4.0, ISS X-Force strongly suggests removing the HTR functionality until such time as a patch is available from Microsoft. If you see a Dr. Watson error or other exception in ISM.DLL, someone is probably trying to attack your host, and it should be assumed that the intrusion was successful. Microsoft Security is developing a patch for this issue and has recommended the following workaround until it becomes available, from Microsoft Security Bulletin MS99-019: 1. From the desktop, start the Internet Service Manager by clicking Start | Programs | Windows NT 4.0 Option Pack | Microsoft Internet Information Server | Internet Service Manager. 2. Double-click "Internet Information Server." 3. Right-click the computer name and select Properties. 4. In the Master Properties drop-down box, select "WWW Service," then click the "Edit" button. 5. Click the "Home Directory" tab, then click the "Configuration" button 6. Highlight the line in the extension mappings that contains ".HTR", then click the "Remove" button. 7. Respond "Yes" to "Remove selected script mapping?", click OK 3 times, and close Internet Service Manager. Acknowledgements This security vulnerability was discovered by the eEye Digital Security Team and subsequently reported to Microsoft Security a week prior to its dissemination on public mailing lists. References eEye Digital Security Team Alert AD06081999: "Retina vs. IIS4, Round 2" at: http://www.eeye.com/database/advisories/ad06081999/ad06081999.html Microsoft Security Bulletin (MS99-019): "Workaround Available for "Malformed HTR Request" Vulnerability" at: http://www.microsoft.com/security/bulletins/ms99-019.asp -----BEGIN PGP SIGNATURE----- Version: 2.6.3a Charset: noconv iQCVAwUBN2mjPzRfJiV99eG9AQFtYgP+LfpJPTdi0v5v+RY8AgUKTV+V29yZA6BO A8177fxk4ZsbqsnsaWrk6S9J7Wg1JdujhjKc5gEQFI80AElLfGxptHoRYYlq+DKW hDitOY0I0YpjIvewGVXTRI6TJnCnt/i//Q2eeIORIVhlu/8Gow23ufg9ymKuFnIC xWCUIuDFW5c= =CFcZ -----END PGP SIGNATURE-----