FedCIRC Advisory FA-98-92
Original issue date: October 14, 1998
Topic: Cisco IOS Command History Release at Login Prompt
To aid in the wide distribution of essential security information, FedCIRC is forwarding the following information from Cisco. Cisco urges you to act on this information as soon as possible. Cisco contact information is included in the forwarded text below; please contact them if you have any questions or need further information.
=======================FORWARDED TEXT STARTS HERE============================ Field Notice: Cisco IOS Command History Release at Login Prompt =================================================================== Revision 1.0 For release 08:00 AM US/Pacific, Wednesday, October 14, 1998 Cisco internal use only until release date. Summary ======= An error in Cisco IOS software makes it possible for untrusted, unauthenticated users who can gain access to the login prompt of a router or other Cisco IOS device, via any means, to obtain fragments of text entered by prior interactive users of the device. This text may contain sensitive information, possibly including passwords. This vulnerability exposes only text entered at prompts issued by the IOS device itself; the contents of data packets forwarded by IOS devices are not exposed, nor are data entered as part of outgoing interactive connections, such as TELNET connections, from the IOS device to other network nodes. This applies only to devices running classic Cisco IOS software, including most, but not all, Cisco router products. The easiest way to determine whether your device is running classic Cisco IOS software is to use the show version command as detailed under "Who Is Affected " below. Although the conditions under which it can be exploited are similar, this vulnerability is not related to the remote crash vulnerability announced in August, 1998. Who Is Affected =============== All users of classic Cisco IOS software, versions 9.1 and later, but earlier than the repaired versions listed in the "Details" section of this notice, whose devices can be connected to interactively by untrusted users, are affected by this vulnerability. Note that all of the repaired versions are quite recent as of the date of this notice, and that it is unlikely that most Cisco users have installed them. The vulnerability affects the vast majority of systems running Cisco IOS software as of this date. The vulnerability can be exploited using direct console or asynchronous serial connections (including dialup connections), TELNET connections, UNIX "r" command connections, LAT connections, MOP connections, X.29 connections, V.120 connections, and possibly others. Except in extraordinary security environments, administrators are strongly encouraged to assume that hostile users can find ways to make interactive connections to their Cisco IOS devices. It is not necessary to be able to actually log in to exploit this vulnerability; simply establishing a terminal connection is sufficient. Affected Devices ================ It is impossible to list all Cisco products in this notice; the lists below included only the most commonly used or most asked-about products. If you are unsure whether your device is running classic Cisco IOS software, log into the device and issue the command show version. Classic Cisco IOS software will identify itself simply as "IOS" or "Internetwork Operating System Software". Other Cisco devices either will not have the show version command, or will give different output. Cisco devices that run classic Cisco IOS software include: * Cisco routers in the AGS/MGS/CGS/AGS+, IGS, RSM, 8xx, 1xxx, 25xx, 26xx, 30xx, 36xx, 40xx, 45xx, 47xx, AS52xx, AS53xx, 70xx, 72xx (including the ubr72xx), 75xx, and 12xxx series * Most recent versions of the LS1010 ATM switch * Some versions of the Catalyst 2900XL LAN switch. * The Cisco DistributedDirector If you are not running classic Cisco IOS software, then you are not affected by this vulnerability. Cisco devices which do not run classic Cisco IOS software, and are not affected by this vulnerability, include the following: * 7xx dialup routers (750, 760, and 770 series) are not affected. * Catalyst 19xx, 28xx, 29xx, 3xxx, and 5xxx LAN switches are not affected, except for some versions of the Catalyst 2900XL. However, optional router modules running Cisco IOS software in switch backplanes, such as the RSM module for the Catalyst 5000 and 5500, are affected. * WAN switching products in the IGX and BPX lines are not affected. * The MGX (formerly known as the AXIS shelf) is not affected. * No host-based software is affected. * The Cisco PIX Firewall is not affected. * The Cisco LocalDirector is not affected. * The Cisco Cache Engine is not affected. Impact ====== If attackers know the details of the Cisco IOS software error, they will be able to obtain fragments of the last few lines of text entered in response to IOS prompts on the physical or virtual TTYs to which they are connected. The exact amount of recoverable text varies, and will be split among fragments of various lines. Nearly complete lines, and fragments tens of characters long, can sometimes be obtained. If the previous session was brief, the available information may include part or all of the password that a previous user used to log into the router or to enable privileged mode. If a previous user changed a system password, such as the enable password, and logged out shortly thereafter, it may be possible to recover the new password by reading the configuration command used to make the change. This vulnerability does not expose anything entered as part of an outgoing session from the IOS device to another node. For example, if a user logs into an IOS router, and then makes a TELNET connection to a remote host, none of the data in the TELNET connection itself can be recovered. Details ======= This vulnerability has been assigned Cisco bug ID CSCdk43920. Affected and Repaired Software Versions ------------------------------------- This vulnerability affects all releases of Classic Cisco IOS software, including special, interim, and beta software, from 9.1 up to, but not including, the following corrected releases: Earliest Regular Releases Earliest Interim Releases ------------------------- ------------------------- 11.0(22) 11.0(21.2) 11.1(22), 11.1(22)CA, 11.1(21)CC1, 11.1(22), 11.1(21.2)CA, 11.1(22)CE 11.1(21)CC1, 11.1(21.1)CE 11.2(16), 11.2(16)P, 11.2(15.4), 11.2(15.4)P, 11.2(16)BC,11.2(8)SA4 11.2(15.4)BC, 11.2(8)SA4 11.3(6), 11.3(6)T, 11.3(6)AA, 11.3(1)MA6, 11.3(5.6), 11.3(5.6)T, 11.3(6)NA, 11.3(9)WA4 11.3(5.6)AA, 11.3(1)MA54, 11.3(5.6)NA 12.0(1), 12.0(1)T, 12.0(1)S, other 12.0 Will be integrated in initial 12.0(1)x releases It is not necessary to run the specific versions listed above; the fix is present in all subsequent versions of the same releases as well. For example, 11.2(16)P is fixed, so 11.2(17)P will also be fixed. The fix is available in all regular releases as of the date of this notice. However, the fix has not yet been released for all "two-letter" early deployment software. Integration is under way for the unreleased "two-letter" versions. Some releases of Cisco IOS software have been obsoleted or have reached end of maintenance. The upgrade paths for the users of these releases are as follows: Obsolete Release Upgrade To ---------------- ---------- 1.x - 8.x, 9.1, 9.14, 9.17, 9.21, 11.0 (be especially careful to check 10.1, 10.2, 10.3 (all variants) hardware compatibility) 11.0BT 11.1 11.1AA 11.2(16)P 11.2(4)XA, 11.2(9)XA 11.2(16)P 11.3(2)XA 11.3(3) 11.2F 11.3(6) Getting Fixed Software -------------------- Cisco is offering free software upgrades to remedy this vulnerability for all vulnerable customers, regardless of contract status. Customers with service contracts may upgrade to any Cisco IOS software version. Customers without contracts may upgrade to the latest versions of the releases and feature sets that they are already running (for example, from 11.2(2) to 11.2(16), but not from 11.2(2) to 11.3(6)). Customers without contracts who are running obsolete software will receive free upgrades to the fixed versions listed in the table above. Furthermore, if there is no immediately available fix for software being run by a customer without a contract, then that customer will immediately be given the most appropriate available fixed software, even if a release or feature upgrade is involved. Customers with contracts should obtain upgraded software through their regular update channels (generally via Cisco's Worldwide Web site). Customers without contracts should get their upgrades by contacting the Cisco TAC. TAC contacts are as follows: * +1 800 553 2447 (toll-free from within North America) * +1 408 526 7209 (toll call from anywhere in the world) e-mail: email@example.com Give the URL of this notice as evidence of your entitlement to a free upgrade. Free upgrades for non-contract customers must be requested through the TAC. Please do not contact either "firstname.lastname@example.org" or "email@example.com" for software upgrades. As with any software upgrade, you should check to make sure that your hardware can support the new software before upgrading. The most common problem is inadequate RAM. Assistance is available on Cisco's Worldwide Web site at http://www.cisco.com. Workarounds --------- There are two major workarounds for this vulnerability: 1. Prevent untrusted users from having interactive access to the Cisco IOS device. If only IP-based interactive access is of concern, access can be restricted by using the ip access-class line configuration command to apply an access list to all virtual terminals in the system. However, it is important to remember that non-IP-based means of making interactive connections to Cisco IOS devices do exist, and to eliminate those means as possible routes of attack. The transport input command is particularly useful in controlling the protocols that can be used to get interactive access. Interactive access can be prevented completely by applying the configuration command no exec to any asynchronous line, or the command transport input none to any virtual terminal line, that may be accessible to untrusted users. 2. Overwrite any potentially sensitive information before logging out of any interactive session on an IOS device. This can be done by entering repeated spaces at an IOS command prompt until the command interpreter will accept no more input on the line, then pressing the "return" key. Follow this by entering a printing character, such as "q", repeatedly until no more input is accepted, then pressing control-A, followed by control-K, then "return" again. This procedure vastly reduces the probability of information leakage, but has not been verified to completely eliminate the possibility in all affected versions of Cisco IOS software. Cisco recommends installing upgraded software in preference to using either of these workarounds. The first workaround should be part of normal security configuration in any Cisco IOS device, but cannot usually be used to eliminate all possible risk, since some interactive access must be available for system management. The second workaround is prone to human error, and, although it greatly reduces the probability of an attacker's finding anything sensitive, it does not completely eliminate that possibility. Exploitation and Public Announcements ===================================== Cisco knows of no public announcements or discussion of the details of this vulnerability prior to the date of this notice. An inadvertant preannouncement was made to certain Cisco customers during the week of October 5, but the only information given to those customers consisted of the bug ID and the bug headline, which was "Security Problem". In other words, they were told that a security problem existed in a version of Cisco IOS software, but were given absolutely no details. A later message to those same customers informed them that the vulnerability had been found by a trusted customer, that Cisco knew of no exploitation of the vulnerability, and that a formal notice would be forthcoming. Extreme care was taken to avoid giving information that could be used to localize the vulnerability to any particular part of the Cisco IOS software, or other information that might be useful in finding the details. Cisco knows of no malicious exploitation of this vulnerability. This vulnerability was found by a Cisco customer during laboratory testing. Status of This Notice ===================== This is a final field notice. Although Cisco cannot guarantee the accuracy of all statements in this notice, all the facts have been checked to the best of our ability. Cisco does not anticipate issuing updated versions of this notice unless there is some material change in the facts. Should there be a significant change in the facts, Cisco may update this notice. Distribution ---------- This notice will be posted on Cisco's Worldwide Web site at http://www.cisco.com/warp/public/770/ioshist-pub.shtml . In addition to Worldwide Web posting, the initial version of this notice is being sent to the following e-mail and Usenet news recipients: * firstname.lastname@example.org * email@example.com * firstname.lastname@example.org (includes CERT/CC) * email@example.com * comp.dcom.sys.cisco * firstname.lastname@example.org * email@example.com * Various internal Cisco mailing lists Future updates of this notice, if any, will be placed on Cisco's Worldwide Web server, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the URL given above for any updates. Revision History -------------- Revision 1.0, 22:30 US/Pacific, Initial released version 11-OCT-1998 Cisco Security Procedures ========================= Please report security issues with Cisco products, and/or sensitive security intrusion emergencies involving Cisco products, to firstname.lastname@example.org . Reports may be encrypted using PGP; public RSA and DSS keys for "email@example.com" are on the public PGP keyservers. The alias "firstname.lastname@example.org" is used only for reports incoming to Cisco. Mail sent to the list goes only to a very small group of users within Cisco. Neither outside users nor unauthorized Cisco employees may subscribe to "email@example.com". Please do not use "firstname.lastname@example.org" for configuration questions, for security intrusions that you do not consider to be sensitive emergencies, or for general, non-security-related support requests. We do not have the capacity to handle such requests through this channel, and will refer them to the TAC, delaying response to your questions. We advise contacting the TAC directly with these requests. TAC contact numbers are as follows: * +1 800 553 2447 (toll-free from within North America) * +1 408 526 7209 (toll call from anywhere in the world) * e-mail: email@example.com All formal public security notices generated by Cisco are sent to the public mailing list "firstname.lastname@example.org". For information on subscribing to this mailing list, send a message containing the single line "info cust-security-announce" to "email@example.com". An analogous list, "firstname.lastname@example.org" is available for public discussion of the notices and of other Cisco security issues. =================================================================== This notice is copyright 1998 by Cisco Systems, Inc. This notice may be redistributed freely after the release date given at the top of the text, provided that redistributed copies are complete and unmodified, including all date and version information. =================================================================== ========================FORWARDED TEXT ENDS HERE=============================
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