============================================================================= CA-95:03 CERT Advisory February 16, 1995 Telnet Encryption Vulnerability ----------------------------------------------------------------------------- The CERT Coordination Center has received reports of a serious security problem in the Berkeley Telnet clients that provide support for the experimental Telnet encryption option using the Kerberos V4 authentication. All known released versions of the BSD Telnet that support Kerberos V4 authentication and encryption are affected. We recommend that all sites that use encrypted telnet in conjunction with Kerberos V4 obtain a patch or upgraded version of Telnet according to the instructions in Section III below. As we receive additional information relating to this advisory, we will place it, along with any clarifications, in a CA-95:03.README file. CERT advisories and their associated README files are available by anonymous FTP from info.cert.org. We encourage you to check the README files regularly for updates on advisories that relate to your site. I. Description There is a vulnerability in Berkeley Telnet clients that support encryption and Kerberos V4 authentications. This vulnerability substantially reduces the effectiveness of the encryption. II. Impact Anyone who can access and read packets that make up the encrypted Telnet session can easily decrypt the session. This is possible, for example, when an intruder uses a packet sniffer on the network to intercept the Telnet sessions. III. Solution Obtain and install the appropriate patch according to the instructions included with the patch. Below is a summary of the vendors who have reported to us and the status they provided. More complete information, including how to obtain patches, is printed in Appendix A of this advisory and reproduced in the README file associated with this advisory. We will update the README file as we receive more information from vendors. Vendor or Source Status ---------------- ------------ Berkeley SW Distribution (BSD) source-code patch available from Berkeley; also in Appendix B of this advisory Data General Corporation not affected by the vulnerability FTP Software, Inc. patch available Harris NightHawk System not affected by the vulnerability Hewlett-Packard Company not affected by the vulnerability Nat'l. Center for Supercomputer Applications (NCSA) upgrade available Open Software Foundation not affected by the vulnerability The Santa Cruz Operation, Inc. (SCO) not affected by the vulnerability Sun Microsystems, Inc. not affected by the vulnerability If you have an encrypting Telnet from some other vendor, please contact that vendor for information regarding how to get a fixed version. --------------------------------------------------------------------------- The CERT Coordination Center wishes to thank Theodore Ts'o of the Massachusetts Institute of Technology for identifying and developing a solution to this problem. --------------------------------------------------------------------------- If you believe that your system has been compromised, contact the CERT Coordination Center or your representative in Forum of Incident Response and Security Teams (FIRST). If you wish to send sensitive incident or vulnerability information to CERT staff by electronic mail, we strongly advise that the e-mail be encrypted. The CERT Coordination Center can support a shared DES key, PGP (public key available via anonymous FTP on info.cert.org), or PEM (contact CERT staff for details). Internet E-mail: cert@cert.org Telephone: +1 412-268-7090 (24-hour hotline) CERT personnel answer 8:30 a.m.-5:00 p.m. EST(GMT-5)/EDT(GMT-4), and are on call for emergencies during other hours. Fax: +1 412-268-6989 CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh, PA 15213-3890 USA Past advisories, CERT bulletins, information about FIRST representatives, and other information related to computer security are available for anonymous FTP from info.cert.org. CERT is a service mark of Carnegie Mellon University. .............................................................................  Appendix A: Vendor Information Current as of February 16, 1995 See CA-95:03.README for updated information. Below is information we have received from vendors who have patches available or upcoming, along with names of vendors who have reported that their products do not have the problem. If you have an encrypting Telnet from a vendor who is not listed, please contact that vendor for information regarding how to get a fixed version. Vendor or Source Status ---------------- ------------ Berkeley SW Distribution (BSD) source-code patch available from Berkeley; also in Appendix B of this advisory Data General Corporation not affected by the vulnerability FTP Software, Inc. patch available Harris NightHawk System not affected by the vulnerability Hewlett-Packard Company not affected by the vulnerability Nat'l. Center for Supercomputer Applications (NCSA) upgrade available Open Software Foundation not affected by the vulnerability The Santa Cruz Operation, Inc.(SCO) not affected by the vulnerability Sun Microsystems, Inc. not affected by the vulnerability PATCH INFORMATION ------------- Berkeley Software Distribution (BSD) A source-code patch, along with the domestic version of the most recently released Telnet sources from Berkeley, are available by anonymous FTP from net-dist.mit.edu:/pub/telnet/telnet.patch MD5 65d56befe3d0f1699d38de5509552578 There is also a PGP ASCII signature file for the patch in net-dist.mit.edu:/pub/telnet/telnet.patch.sig This patch can also be found in CERT Advisory CA-95:03, Appendix B. (Note: Do not calculate a checksum for Appendix B alone. It will not match the checksum of the FTP version of the patch because the tabs in the FTP copy have been replaced with blank spaces in the CA-95:03 Appendix B copy.) ------------- FTP Software, Inc. Customers of FTP Software with an encrypting telnet (provided in the PC/TCP or OnNet packages) should call the FTP technical support line at 1-800-282-4387 and ask for the "tn encrypt patch". ------------- National Center for Supercomputer Applications (NCSA) Users of NCSA Telnet should upgrade to the NCSA Telnet 2.6.1d7, AND install the appropriate Kerberos plug-in which are available by anonymous FTP from ftp.ncsa.uiuc.edu Upgrade /Mac/Telnet/Telnet2.6/prerelease/d7/Telnet2.6.1d7(68K).sit.hqx MD5 b34b9fda59421b3b83f8df08a83f83b5 /Mac/Telnet/Telnet2.6/prerelease/d7/Telnet2.6.1d7(fat).sit.hqx MD5 877add7c3d298111889fc3f2f272ce6f Kerberos plug-ins /Mac/Telnet/Telnet2.6/prerelease/AuthMan.plugin.1.0b1.hqx MD5 df727eae184b22125f90ef1a31513fd4 /Mac/Telnet/Telnet2.6/prerelease/Kerberos_Telnet_plugin.sit.hqx MD5 dbda691efe9038648f234397895c734d Questions regarding NCSA Telnet should be directed to mactel@ncsa.uiuc.edu .............................................................................  Appendix B: Patch for Vulnerability in Telnet Encryption Option Current as of February 16, 1995 See CA-95:03.README for updated information. Index: auth.c =================================================================== RCS file: /mit/krb5/.cvsroot/src/appl/telnet/libtelnet/auth.c,v retrieving revision 5.5 retrieving revision 5.7 diff -u -r5.5 -r5.7 --- auth.c 1994/08/18 21:06:45 5.5 +++ auth.c 1994/11/08 04:39:02 5.7 @@ -244,7 +244,7 @@ { register int x; - if (strcasecmp(type, AUTHTYPE_NAME(0))) { + if (!strcasecmp(type, AUTHTYPE_NAME(0))) { *maskp = -1; return(1); } @@ -260,14 +260,14 @@ int auth_enable(type) - int type; + char * type; { return(auth_onoff(type, 1)); } int auth_disable(type) - int type; + char * type; { return(auth_onoff(type, 0)); } @@ -277,15 +277,20 @@ char *type; int on; { - int mask = -1; + int i, mask = -1; Authenticator *ap; if (!strcasecmp(type, "?") || !strcasecmp(type, "help")) { printf("auth %s 'type'\n", on ? "enable" : "disable"); printf("Where 'type' is one of:\n"); printf("\t%s\n", AUTHTYPE_NAME(0)); - for (ap = authenticators; ap->type; ap++) + mask = 0; + for (ap = authenticators; ap->type; ap++) { + if ((mask & (i = typemask(ap->type))) != 0) + continue; + mask |= i; printf("\t%s\n", AUTHTYPE_NAME(ap->type)); + } return(0); } @@ -293,7 +298,6 @@ printf("%s: invalid authentication type\n", type); return(0); } - mask = getauthmask(type, &mask); if (on) i_wont_support &= ~mask; else @@ -317,16 +321,22 @@ auth_status() { Authenticator *ap; + int i, mask; if (i_wont_support == -1) printf("Authentication disabled\n"); else printf("Authentication enabled\n"); - for (ap = authenticators; ap->type; ap++) + mask = 0; + for (ap = authenticators; ap->type; ap++) { + if ((mask & (i = typemask(ap->type))) != 0) + continue; + mask |= i; printf("%s: %s\n", AUTHTYPE_NAME(ap->type), (i_wont_support & typemask(ap->type)) ? "disabled" : "enabled"); + } return(1); } Index: kerberos.c =================================================================== RCS file: /mit/krb5/.cvsroot/src/appl/telnet/libtelnet/kerberos.c,v retrieving revision 5.5 retrieving revision 5.8 diff -u -r5.5 -r5.8 --- kerberos.c 1994/08/18 21:07:02 5.5 +++ kerberos.c 1994/11/14 21:33:58 5.8 @@ -225,9 +225,10 @@ register int i; des_key_sched(cred.session, sched); - des_set_random_generator_seed(cred.session); - des_new_random_key(challenge); - des_ecb_encrypt(challenge, session_key, sched, 1); + des_init_random_number_generator(cred.session); + des_new_random_key(session_key); + des_ecb_encrypt(session_key, session_key, sched, 0); + des_ecb_encrypt(session_key, challenge, sched, 0); /* * Increment the challenge by 1, and encrypt it for * later comparison. @@ -320,6 +321,11 @@ break; }