-----BEGIN PGP SIGNED MESSAGE----- ============================================================================= CERT(sm) Advisory CA-96.10 Original issue date: May 28, 1996 Last revised: August 30, 1996 Information previously in the README was inserted into the advisory. A complete revision history is at the end of this file. Topic: NIS+ Configuration Vulnerability - ----------------------------------------------------------------------------- The text of this advisory was originally released by the Australian Emergency Response Team on May 20, 1996, and updated on May 27, 1996, as AUSCERT advisory AA-96.02a. Because of the seriousness of the problem, we are reprinting the AUSCERT advisory here with their permission. Only the contact information at the end has changed: AUSCERT contact information has been replaced with CERT/CC contact information. We will update this advisory as we receive additional information. Please check advisory files regularly for updates that relate to your site. ============================================================================= 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. ** This updated advisory contains clarifications for sites requiring password ** aging facilities and sites running their NIS+ servers in NIS compatibility ** mode. - ----------------------------------------------------------------------------- 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. However, depending on the local site configuration and requirements, additional access rights may also be needed. - Sites that wish users to be able to change their shell or gcos information may have the (m)odify bit set for owner on the shell or gcos column as needed. - Sites that have their NIS+ servers running in NIS compatibility mode to serve NIS clients may require (r)ead permission for nobody on the NIS+ passwd table. - Sites that are using password aging may require additional access rights on the shadow column. The exact access rights will depend on the particular NIS+ version (including patches). Sites are encouraged to check their local documentation for more information. Other than this, the access rights on columns should appear as shown in the niscat(1) output 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. ============================================================================= CERT Contact Information - ------------------------ If you believe that your system has been compromised, contact the CERT Coordination Center or your representative in the Forum of Incident Response and Security Teams (FIRST). We strongly urge you to encrypt any sensitive information you send by email. The CERT Coordination Center can support a shared DES key and PGP. Contact the CERT staff for more information. Location of CERT PGP key ftp://info.cert.org/pub/CERT_PGP.key Email cert@cert.org Phone +1 412-268-7090 (24-hour hotline) CERT personnel answer 8:30-5:00 p.m. EST (GMT-5)/EDT(GMT-4), and are on call for emergencies during other hours. Fax +1 412-268-6989 Postal address CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh PA 15213-3890 USA CERT publications, information about FIRST representatives, and other security-related information are available for anonymous FTP from http://www.cert.org/ ftp://info.cert.org/pub/ CERT advisories and bulletins are also posted on the USENET newsgroup comp.security.announce To be added to our mailing list for CERT advisories and bulletins, send your email address to cert-advisory-request@cert.org Copyright 1996 Carnegie Mellon University This material may be reproduced and distributed without permission provided it is used for noncommercial purposes and the copyright statement is included. CERT is a service mark of Carnegie Mellon University. ============================================================================== UPDATES CERT/CC received information concerning an additional problem with the ROW access rights in the NIS+ password table. Accounts created on Solaris 2.4 and 2.5 systems have excessive rights on the system. These new super accounts have read, modify, create, and delete access rights on their own rows in the nisplus password table. This means they can alter all attributes on their own entries. To determine if your system is so affected, execute the following: % niscat -o '[name=juke],passwd.org_dir' | egrep "Access" If the output displays information similar to the following: Access Rights : ----rmcdr---r--- ^^^^ then the owner can read, modify, change, and delete information. The rights at this level should be more restrictive, and the individual rights on entries should be less restrictive. The less restrictive rights on entries allow a user to change their password entry, the GECOS field, and even the shell depending upon how the entry rights are set. The output from the niscat above should look like the following: Access Rights : ----r----------- This allows only the user to read information from the password table. One way to determine which entries in the password table need to be changed is the following: % niscat -o '[ ],passwd.org_dir' | egrep "Owner|rmc" To fix the entries, use the following: % nischmod o=r,ngw-rmdc '[ ],passwd.org_dir' This sets the owner permissions to r (read) and removes all permissions from nobody, group, and world. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Revision history Aug. 30, 1996 Information previously in the README was inserted into the advisory. Beginning of the advisory - removed AUSCERT advisory header to avoid confusion. June 12, 1996 Updates section - added clarification concerning ROW access rights. -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBMiTCFnVP+x0t4w7BAQGCNgP9HzQyAGwZKH0XxXctYdq6u+9I9QPkAmG9 BGpgug7ZFcL1P+9R/M+1yOCMS4UScwiTeaeT3iMb0uCXeKmEUtC526uv7eLqb1RA GeT8+BAkAym943l/LOpnfmUJgCWHKv39DZJXUym5SWM9BpDwPW+u0eIsoycNuhWZ Qa5aDuncx7o= =GFo0 -----END PGP SIGNATURE-----