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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2006.0917 -- [UNIX/Linux] GNOME Foundation Display Manager gdmchooser Format String Vulnerability 15 December 2006 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: gdmchooser Publisher: iDEFENSE Operating System: UNIX variants (UNIX, Linux, OSX) Impact: Execute Arbitrary Code/Commands Access: Console/Physical CVE Names: CVE-2006-6105 Original Bulletin: http://labs.idefense.com/intelligence/vulnerabilities/display.php?id=453 - --------------------------BEGIN INCLUDED TEXT-------------------- GNOME Foundation Display Manager gdmchooser Format String Vulnerability iDefense Security Advisory 12.14.06 http://labs.idefense.com/intelligence/vulnerabilities/ Dec 14, 2006 I. BACKGROUND The gdmchooser program provides XDMCP (X Display Manager Control Protocol) functionality to the GNOME Display Manager. This protocol allows a user to interact remote systems via the local X11 display. II. DESCRIPTION Local exploitation of a format string vulnerability in GNOME Foundation's GNOME Display Manager host chooser window (gdmchooser) could allow an unauthenticated attacker to execute arbitrary code on the affected system. The vulnerability specifically exists in the handling of values entered when choosing a remote host to connect to from the current system. The following snippet from gdmchooser.c shows the vulnerable code: 1395 msg = g_strdup_printf (_("Cannot find the host \"%s\". " 1396 "Perhaps you have mistyped it."), 1397 name); 1398 1399 dialog = ve_hig_dialog_new 1400 (GTK_WINDOW (chooser) /* parent */, 1401 GTK_DIALOG_MODAL /* flags */, 1402 GTK_MESSAGE_ERROR, 1403 GTK_BUTTONS_OK, 1404 _("Cannot find host"), 1405 msg); 1406 1407 g_free (msg); 1408 The error dialog uses the temporary value 'msg', constructed from 'name' when the host is not found. By supplying a sequence of formatting operations which modify memory values, an unauthenticated attacker can execute code with the permissions under the gdm account. III. ANALYSIS Successful local exploitation of this vulnerability would allow an unauthenticated attacker to execute arbitrary code with the privileges of the gdm service. In order to exploit this vulnerability, the attacker would need to have access to the system running gdmchooser. Connecting remotely to this service will not work as the functionality is designed to connect to a remote server already, and proxying is not allowed. The attacker selects the option to run the gdmchooser, and then types the format string into the dialog box. They can send a string which displays the contents of the stack, and use there construct a format string which will write controlled values to arbitrary memory locations, which allows execution of code with the privileges of the gdmchooser, typically the user 'gdm'. Although this user does not have a high privilege level, once this account has been gained, it would be relatively simple to insert a logger into gdm processes to capture other users passwords. The gdmchooser is not accessible from the default login screens in any of the tested Red Hat systems, however the preferences utility does contain some preset screens which do contain it. IV. DETECTION This vulnerability has been confirmed to exist in the gdm-2.14.1-1 RPM from Red Hat Fedora Core 5. The vulnerability was introduced into the gdmchooser.c file in version 1.78 of gdm2/gui/gdmchooser.c in the GNOME CVS source code repository. V. WORKAROUND If XDMCP functionality is not required, setting the permissions on the gdmchooser to not allow execution will prevent any attempts at exploitation. VI. VENDOR RESPONSE The GNOME maintainers have addressed this problem by releasing versions 2.14.11, 2.16.4, and 2.17.4 of the GNOME Display Manager. VII. CVE INFORMATION The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2006-6105 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 12/04/2006 Initial vendor notification 12/05/2006 Initial vendor response 12/14/2006 Coordinated public disclosure IX. CREDIT The discoverer of this vulnerability wishes to remain anonymous. Get paid for vulnerability research http://labs.idefense.com/methodology/vulnerability/vcp.php Free tools, research and upcoming events http://labs.idefense.com/ X. LEGAL NOTICES Copyright © 2006 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 e-mail customerservice@idefense.com 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. - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. NOTE: Third Party Rights This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. 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Previous advisories and external security bulletins can be retrieved from: http://www.auscert.org.au/render.html?cid=1980 If you believe that your computer system has been compromised or attacked in any way, we encourage you to let us know by completing the secure National IT Incident Reporting Form at: http://www.auscert.org.au/render.html?it=3192 =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane Qld 4072 Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iQCVAwUBRYHycCh9+71yA2DNAQJtOAP+I6/HgO3heOLuv2X3F0yrMuAKmki9WDzO YY1QXHyKPbiYtxmz5IQEQnEqnIE18vnpmadJu4sZm7792QmmzeT3l1b6KbewHgLJ 77ARcFke08eDIH1odiwR+r8JyDrDRdn2Mx5/X26TK/2MyqplWkUjOIkPasnYpnw6 GGjZpEe+YZI= =qeS0 -----END PGP SIGNATURE-----