Forwarded From: RSI Advise <adviseat_private> RSI.0008.08-18-98.ALL.RPC_PCNFSD |:::. |::::: |::::. |::::: |::::: |::::. .. :: .. .. :: .. .. .. :: |:::: |:::: |:::: :::::: |::::: |:::: |: |: :: |: |: |:: |: |: :: |: :: |::::: |: |::::: |::::: |::::: Repent Security Incorporated, RSI [ http://www.repsec.com ] *** RSI ALERT ADVISORY *** --- [CREDIT] -------------------------------------------------------------- 'Bermuda Brian': Research and development Mark Zielinski : Author of advisory --- [SUMMARY] ------------------------------------------------------------- Announced: July 14, 1998 Report code: RSI.0008.08-18-98.ALL.RPC_PCNFSD Report title: All rpc.pcnfsd Vulnerability: Please see the details section Vendor status: IBM contacted on August 3, 1998 Hewlett Packard contacted on August 3, 1998 Sun Microsystems contacted on August 3, 1998 Slackware contacted on August 3, 1998 Patch status: Linux and AIX patch information is provided below Platforms: Vulnerable: AIX: 4.0, 4.1, 4.2, 4.3 HP-UX: 7.x, 8.x, 9.x, 10.x, 11.x SunOS: 4.1.3, 4.1.4 Solaris: 2.3, 2.4, 2.5, 2.5.1, 2.6 Redhat Linux: 4.0, 4.1, 4.2, 5.0, 5.1 Slackware Linux: 3.0, 3.1, 3.2, 3.3, 3.4, 3.5 OSF: 3.2 Not vulnerable: OpenBSD, FreeBSD, NetBSD, BSDI Reference: http://www.repsec.com/advisories.html Impact: If exploited, an attacker could potentially compromise root access both locally and remotely on your server --- [DETAILS] ------------------------------------------------------------- Description: PCNFSD is a Remote Procedure Call used by NFS clients. This service provides username and password authentication for networked computers which have installed NFS client software. Problem: Two vulnerabilities are covered in this advisory which both allow root access to be compromised. Vulnerable functions: ~~~~~~~~~~~~~~~~~~~~~ A. pr_init () : This function will create a spool directory for a client. When passing data to this function, it calls secure () attempting to find any insecure characters. The list of characters that suspicious () checks for are: ";|&<>`'!?*()[]^/". By sending a "." as the printer name, rpc.pcnfsd will attempt to make that directory and set the mode to 777. By doing this, an attacker sets the main spool directory used by rpc.pcnfsd to world writeable. To exploit this, an attacker could locally set a symbolic link from /var/spool/pcnfsd/printername to any other file on the system. Calling pr_init () with the name of the symbolically linked file will force rpc.pcnfsd to follow the symlink and change the destination file to mode 777. B. run_ps630 () : Upon system bootup, rpc.pcnfsd is started from the system rc files which are executed from the / directory. Because of this, rpc.pcnfsd will attempt to function out of the root directory (/). When run_ps630 () is called, it calls suspicious () to check for any insecure characters. The list of characters that secure () checks for are: ";|&<>`'!?*()[]^/". If it detects that none of these characters are being used, it will call strcat () to append the data to a buffer and then run the data contained inside it with system (). By sending a \ncommand\n as the printer, "." as the spool directory, and setting your client options to "d", arbitary commands can be executed remotely on the server as root. * Note : AIX is not vulnerable to problem A, and HP is only vulnerable to function A in HP-UX 9.0, 10.0. --- [FIX] ----------------------------------------------------------------- Solution: Disable rpc.pcnfsd until an appropriate patch is released for your operating system. --- [AIX PATCH] ----------------------------------------------------------- AIX users: IBM has provided the following patches in reponse to this vulnerability: APAR 4.1.x: IX81505 APAR 4.2.x: IX81506 APAR 4.3.x: IX81507 Until the official APARs are available, a temporary fix can be downloaded via anonymous ftp from: ftp://aix.software.ibm.com/aix/efixes/security/pcnfsd.tar.Z --- [LINUX PATCH] --------------------------------------------------------- Solution: Working in conjunction with Patrick Volkerding and the Slackware Linux development staff, RSI has produced the following patches: ftp://ftp.repsec.com/pub/repsec/0008.patch1 WARNING! The code quoted below is only fragments of each patch! You must download each patch for it to work correctly. 0008.patch1 replaces the character set that is considered suspicious and replaces it with a list of characters that are allowed. The following two lines show the change: [snip...] - if(strpbrk(s, ";|&<>`'#!?*()[]^/") != NULL) [snip...] + if (strspn(s, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_=:+1234567890@%,.") [snip...] --- ftp://ftp.repsec.com/pub/repsec/0008.patch2 0008.patch2 replaces the vulnerable code by removing the chmod call, and utilizing umask. The following code fragments have been stripped out of the patch to show the vulnerable pieces of code and the relevant fix. [snip...] + oldumask = umask(0); + (void)sprintf(pathname,"%s/%s",sp_name, sys); + (void)mkdir(sp_name, dir_mode); /* ignore the return code */ + rc = mkdir(pathname, dir_mode); /* DON'T ignore this return code */ + umask(oldumask); [snip...] - (void)chmod(sp_name, dir_mode); if((rc < 0 && errno != EEXIST) || - (chmod(pathname, dir_mode) != 0) || (stat(pathname, &statbuf) != 0) || !(statbuf.st_mode & S_IFDIR)) { (void)sprintf(tempstr, --- [OTHER PATCHES] ------------------------------------------------------- SunOS, Solaris, HPUX, and OSF users should wait for their respective vendor to provide a patch. --------------------------------------------------------------------------- Repent Security Incorporated (RSI) 13610 N. Scottsdale Rd. Suite #10-326 Scottsdale, AZ 85254 E-Mail: adviseat_private FTP: ftp://ftp.repsec.com WWW: http://www.repsec.com --------------------------------------------------------------------------- -----BEGIN PGP PUBLIC KEY BLOCK----- Version: 2.6.2 mQCNAzU6dqAAAAEEAOHt9a5vevjD8ZjsEmncEbFp2U7aeqvPTcF/8FJMilgOVp75 dshXvZixHsYU7flgCNzA7wLIQPWBQBrweLG6dx9gE9e5Ca6yAJxZg8wNsi06tZfP nvmvf6F/7xoWS5Ei4k3YKuzscxlyePNNKws6uUe2ZmwVoB+i3HHT44dOafMhAAUT tBpSZXBTZWMgPGFkdmlzZUByZXBzZWMuY29tPg== =ro8H -----END PGP PUBLIC KEY BLOCK----- Copyright August 1998 RepSec, Inc. The information in this document is provided as a service to customers of RepSec, Inc. Neither RepSec, Inc., nor any of it's employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process contained herein, or represents that its use would not infringe any privately owned rights. 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Mark Zielinski -----BEGIN PGP PUBLIC KEY BLOCK----- Version: 2.6.2 mQCNAzWmhPkAAAEEAKKFxAIWa6E/ey+3MU8EbeU8pBNXHJOu58weDb7LMHS/QbTF +kvZAWPz+BCMIBBnUn00N8WHm6wqFWG37f5IAzuXm1jy1WX8goCSSW/mpoFZUxxI avKfOc+NHAaeg6uRssIYZhvqlgQkb62JOQivHa/G8UgLdnBfnarRFJ9FQ825AAUR tA5NYXJrIFppZWxpbnNraQ== =B9D6 -----END PGP PUBLIC KEY BLOCK----- -o- Subscribe: mail majordomoat_private with "subscribe isn". Today's ISN Sponsor: New Dimensions International [www.newdimensions.net]
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