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Secure Networks Inc.
in conjunction with
CORE SDI S.A.
Security Advisory
March 23, 1998
Security Issues in Sun NIS+
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SYNOPSIS
The Network Information Server Plus (NIS+) is a network directory service
that provides management and resource location support (including
authentication and name resolution) to heterogenous distributed systems.
Due to implementation problems, the programs supporting NIS+ can be
exploited by an attacker to recover various pieces of system status
information.
It is important to understand that the issues highlighted in this advisory
present no immediate threat of remote compromise; with one exception (the
ability to disable NIS+ logging remotely), all the vulnerabilities
discussed in this advisory do nothing but leak system status and
configuration information. Because NIS+ is a security-critical service,
however, any security issues discovered in it are worth attention.
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DESCRIPTION
NIS+, which replaces the original NIS (also known as "YP"), is made
available to a network via the ONC RPC mechanism, which allows NIS+
clients to interact with the server using remote procedure calls over a
network. The principle server program that supports this is "rpc.nisd",
the RPC NIS+ daemon.
Because the services provided by NIS+ are security-critical, NIS+
is designed to operate securely. An aspect of this design is the concept
of "security levels", which determine the amount of scrutiny given to
incoming RPC NIS requests.
There are three security levels, numbered 0 through 2. In level 0, the
NIS+ server (rpc.nisd) performs no authentication to determine the
legitimacy of incoming requests. This option is provided for debugging
purposes. In level 1, RPC AUTH_UNIX (client-presented UIDs and GIDs)
are used to authenticate requests. In level 2, the most secure level,
AUTH_DES is used to cryptographically authenticate incoming requests.
Unfortunately, even when the system is operating in security level 2,
which should mandate cryptographic authentication for all requests, the
rpc.nisd daemon provides several RPC calls that are not authenticated.
These calls allow a remote client to obtain sensitive system status
information from the NIS+ server.
The information available to a remote attacker includes NIS+ configuration
information (including the security level of the server and a list of
directory objects served by it), as well as the ability to determine valid
process IDs on the NIS+ server.
Additionally, one of the RPC calls available to remote clients can allow
an attacker to disable logging on the NIS+ server, as well as to
manipulate the NIS+ caches. This may allow attackers to degrade or deny
service on NIS+ servers.
The ability to use NIS+ to remotely ascertain valid process IDs is serious
because it allows an attacker the ability to predict certain random
numbers generated by Unix applications. Frequently, Unix applications
generate random numbers using the process ID and the current time, either
directly or as a seed to a random number generator.
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TECHNICAL DETAILS
Three remote procedure calls made available by the NIS+ daemon "rpc.nisd"
have been identified. These are:
A. NIS_CALLBACK
Using the NIS_CALLBACK RPC, arbitrary clients can determine the validity
of a given PID (or, using multiple queries, to map out the identities of
all valid process IDs).
B. NIS_STATUS
Using the NIS_STATUS RPC, arbitrary clients can obtain information about
the NIS+ server configuration, including:
1. The server security level.
2. Whether the server is operating in NIS/YP compatibility mode.
3. Whether the server is a root NIS+ server.
4. Whether it is using it's own DNS resolver or forwarding DNS requests.
5. The list of all directory objects provided by this server.
C. NIS_SERVSTATE
Using the TAG_DEBUG option to this RPC, any remote user can turn off all
rpc.nisd logging. Using the TAG_*CACHE (D, for directory, T, for table,
and G, for group) option, the directory, table, and group caches can be
flushed.
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VULNERABLE SYSTEMS
Solaris 2.x systems up to Solaris 2.5.1, making use of the Network
Information Service Plus (NIS+) system, are vulnerable to these problems.
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RESOLUTION
These problems can be worked around using packet filters to block UDP
traffic to the NIS+ server. Blocking UDP to the NIS+ server from valid
NIS+ clients will cause the NIS+ system to fail.
SunSoft has been notified of this problem and is working on a fix.
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ADDITIONAL INFORMATION
These problems were originally identified by CORE SDI S.A., an
Argentina-based computer security organization, in February of 1997.
More information about the NIS+ system is available in a technical
paper from SunSoft entitled "Network Information Service Plus (NIS+)", by
Chuck McManis and Saqib Jang. The paper is available at:
http://opcom.sun.ca/pub/docs/solaris/NISPlus.ps.Z
A list of frequently asked questions is available at:
http://ee.sun.ac.kr/~ramdrive/NIS+_FAQ.html
CERT Advisory CA-96.10 details a vulnerability in the NIS+ stemming
from improper configuration of password table permissions. The advisory
reprints AUSCERT Advisory AA-96.02. CERT advisories are available at
http://www.cert.org
A Spanish-language NIS+ reference is available at:
http://a01-unix.uc3m.es/~pduenas/nisplus.html
Further questions about this advisory can be addressed to Emiliano
Kargieman <ekat_private> and Ivan Arce at
<ivanat_private>.
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ABOUT SECURE NETWORKS, INC.
Secure Networks, Inc. (SNI) is a security research and development company
based in Calgary, Alberta, Canada. SNI is the largest independent source
of full-disclosure security advisories and new vulnerability information
in the world. For more information about this or other advisories, contact
us at <sniat_private>. A PGP key is provided if privacy is required.
For the full text of this and all of SNI's other advisories, see our web
page at "http://www.secnet.com/advisories/". General information about SNI
is available at "http://www.secnet.com".
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COPYRIGHT INFORMATION
he contents of this advisory are Copyright (C) 1998 Secure Networks
Inc, and may be distributed freely provided that no fee is charged for
distribution, and that proper credit is given.
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Type Bits/KeyID Date User ID
pub 1024/9E55000D 1997/01/13 Secure Networks Inc. <sniat_private>
Secure Networks <securityat_private>
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