From darrenr@cyber.com.au Tue May 21 02:05:23 1996 Received: from plum.cyber.com.au (plum.cyber.com.au [203.7.155.24]) by suburbia.net (8.7.4/Proff-950810) with SMTP id CAA15013 for ; Tue, 21 May 1996 02:05:15 +1000 Received: (from darrenr@localhost) by plum.cyber.com.au (8.6.12/8.6.6) id CAA03135 for best-of-security@suburbia.net; Tue, 21 May 1996 02:04:48 +1000 Received: from satay.cyber.com.au (satay.cyber.com.au [203.7.155.20]) by plum.cyber.com.au (8.6.12/8.6.6) with ESMTP id OAA01994 for ; Mon, 20 May 1996 14:16:53 +1000 From: auscert@auscert.org.au Received: (from uucp@localhost) by satay.cyber.com.au (8.7.4/8.7.3) id OAA08010 for ; Mon, 20 May 1996 14:09:06 +1000 (EST) Received: from onyx0.auscert.org.au(203.5.112.10) by satay.cyber.com.au via smap (V1.3) id sma008007; Mon May 20 14:08:30 1996 Received: from amethyst.auscert.org.au (amethyst.auscert.org.au [203.5.112.218]) by onyx.auscert.org.au (8.7.5/8.7.1) with ESMTP id OAA10817; Mon, 20 May 1996 14:15:49 +1000 (EST) Received: (from eric@localhost) by amethyst.auscert.org.au (8.7.5/8.7.2) id OAA27831; Mon, 20 May 1996 14:15:06 +1000 (EST) Date: Mon, 20 May 1996 14:15:06 +1000 (EST) Message-Id: <199605200415.OAA27831@amethyst.auscert.org.au> To: auscert-public@auscert.org.au Sender: darrenr@cyber.com.au Reply-To: auscert@auscert.org.au Errors-To: postmaster@auscert.org.au Subject: AA-96.02 NIS+ configuration vulnerability Precedence: list -----BEGIN PGP SIGNED MESSAGE----- ============================================================================= AA-96.02 AUSCERT Advisory NIS+ configuration vulnerability 20 May 1996 - ----------------------------------------------------------------------------- AUSCERT has received information that a vulnerability exists under some configurations of NIS+. In vulnerable installations of NIS+, the access rights on the NIS+ passwd table are left in an unsecure state. This vulnerability is known to exist in NIS+ installations initially created on Solaris 2.5 servers. Similar vulnerabilities in NIS+ configurations may also exist in previous versions of Solaris 2. This vulnerability may allow any user with valid NIS+ credentials to gain root privileges. AUSCERT recommends that any site which has NIS+ installed take this opportunity to check their installations and apply the appropriate workarounds as described in Section 3. - ----------------------------------------------------------------------------- 1. Description NIS+ provides distributed network access to information sources such as password, group and host information. It maintains this information in the form of NIS+ tables. NIS+ tables contain the administrative information normally supplied by local files (such as /etc/passwd). As with the standard Unix administration files, setting secure permissions on the NIS+ tables is of utmost importance in maintaining system security. NIS+ provides a comprehensive set of access rights for NIS+ tables. This includes permissions not only on NIS+ tables but also individual columns and entries in those tables. Due to the added complexity, sites need to be particularly diligent in ensuring that permissions on NIS+ tables (and associated entries and columns) are secure. AUSCERT encourages sites running NIS+ to gain a good understanding of the permission model used by NIS+. A complete description may be found in the NIS+ documentation set. The rest of this advisory assumes a good understanding of NIS+ permission controls. AUSCERT has received information that under some installations of NIS+ the permissions on the NIS+ passwd table are left in an unsecure state. This vulnerability is known to exist in NIS+ installations initially created on Solaris 2.5 servers. Similar vulnerabilities in NIS+ configurations may also exist in previous versions of Solaris 2. 2. Impact Any user with login access to a client or server that uses NIS+ for authentication may gain root privileges. 3. Workarounds NIS+ uses an access control mechanism for granting access to NIS+ tables which is similar (but not identical) to that used by the standard Unix file system. NIS+ tables are assigned permissions for the NIS+ user categories nobody, owner, group and world. NIS+ also has permissions associated with columns and individual entries in NIS+ tables. Under some installations of NIS+ the permissions of the NIS+ passwd table and its columns are left in an unsecure state. These permissions can be viewed using niscat(1). To check the permissions on the NIS+ passwd table, sites can use: # niscat -o passwd.org_dir This should produce output similar to: Object Name : passwd Owner : myhost.mydomain.org. Group : admin.mydomain.org. Domain : org_dir.mydomain.org. Access Rights : ----rmcdrmcd---- Time to Live : 12:0:0 Object Type : TABLE Table Type : passwd_tbl Number of Columns : 8 Character Separator : : Search Path : Columns : [0] Name : name Attributes : (SEARCHABLE, TEXTUAL DATA, CASE SENSITIVE) Access Rights : r--------------- [1] Name : passwd Attributes : (TEXTUAL DATA) Access Rights : -----m---------- [2] Name : uid Attributes : (SEARCHABLE, TEXTUAL DATA, CASE SENSITIVE) Access Rights : r--------------- [3] Name : gid Attributes : (TEXTUAL DATA) Access Rights : r--------------- [4] Name : gcos Attributes : (TEXTUAL DATA) Access Rights : r--------------- [5] Name : home Attributes : (TEXTUAL DATA) Access Rights : r--------------- [6] Name : shell Attributes : (TEXTUAL DATA) Access Rights : r--------------- [7] Name : shadow Attributes : (TEXTUAL DATA) Access Rights : ---------------- This output shows two types of access rights associated with the NIS+ passwd table. First, the default access rights for the table, which are given at the start of the output (----rmcdrmcd----). Second, the access rights associated with each column. In particular, sites should check the access rights on the columns of the NIS+ passwd table. It should be noted that it appears that individual entries of the passwd table are owned by individual users. The above access rights do not allow a user to modify any part of their passwd table entry besides their own passwd field. For many environments this is acceptable. For sites who wish users to be able to change their shells or gcos information those columns may have the (m)odify bit set for owner. Other than this, the access rights on columns should appear as above. Any additional access rights on the table or its columns besides those shown above may allow a user to gain additional privileges, including possibly root. Sites should completely understand the ramifications if they allow additional access rights. Sites may set the access rights on the NIS+ passwd table, as shown in the above output, by issuing the following commands as root on the master NIS+ server. To set the default access rights for the NIS+ passwd table: # nischmod na-rmcd,og+rmcd passwd.org_dir To set the column access rights on the NIS+ passwd table: # nistbladm -u name=na-rmcd,n=r passwd.org_dir # nistbladm -u passwd=na-rmcd,o=m passwd.org_dir # nistbladm -u uid=na-rmcd,n=r passwd.org_dir # nistbladm -u gid=na-rmcd,n=r passwd.org_dir # nistbladm -u gcos=na-rmcd,n=r passwd.org_dir # nistbladm -u home=na-rmcd,n=r passwd.org_dir # nistbladm -u shell=na-rmcd,n=r passwd.org_dir # nistbladm -u shadow=na-rmcd passwd.org_dir After making any changes in access rights, AUSCERT recommends that sites verify the changes they have made using niscat(1), as shown previously. Sites that have replica NIS+ servers may use nisping(1m) to propagate the changes to the replica servers in a timely manner. 4. Additional measures AUSCERT recommends that sites take this opportunity to ensure that all NIS+ tables have access rights in accordance with the local site security policy. This also includes checking access rights on all the columns and entries of the NIS+ tables in addition to the default access rights of the tables themselves. - ----------------------------------------------------------------------------- AUSCERT wishes to thank Ivan Angus and David Clarke of ANU for reporting this vulnerability and for their advice in the preparation of this advisory. AUSCERT also acknowledges Marek Krawus of UQ, Reinhard Uebel and Mark McPherson of QTAC for their assistance. - ----------------------------------------------------------------------------- The AUSCERT team have made every effort to ensure that the information contained in this document is accurate. However, the decision to use the information described is the responsibility of each user or organisation. The appropriateness of this document for an organisation or individual system should be considered before application in conjunction with local policies and procedures. AUSCERT takes no responsibility for the consequences of applying the contents of this document. If you believe that your system has been compromised, contact AUSCERT or your representative in FIRST (Forum of Incident Response and Security Teams). AUSCERT is located at The University of Queensland within the Prentice Centre. AUSCERT is a full member of the Forum of Incident Response and Security Teams (FIRST). AUSCERT maintains an anonymous FTP service which is found on: ftp://ftp.auscert.org.au/pub/. This archive contains past SERT and AUSCERT Advisories, and other computer security information. AUSCERT also maintains a World Wide Web service which is found on: http://www.auscert.org.au/. Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 4477 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 emergencies. Postal: Australian Computer Emergency Response Team c/- Prentice Centre The University of Queensland Brisbane Qld. 4072. AUSTRALIA -----BEGIN PGP SIGNATURE----- Version: 2.6.2i Comment: Finger pgp@ftp.auscert.org.au to retrieve AUSCERT's public key iQCVAwUBMaB9dSh9+71yA2DNAQFW5wP9FmRtDwhGOy/0j6tV43zyQ/FjpzRFe3Yv 6Nm37T/iBM1tR6rA0Gbb3Y2idi18lu/zuOFlpsrkccPnT0znAsEFCDkaZ3GjOyLf QExXdRJ1e1Azbsdr9GD1gJ+Ch82jxrlcbUlGcqsvdu7r6re9HMSa5uVLCsXRVhRz M4t+L3kbDF8= =skmB -----END PGP SIGNATURE-----