Package: lrzsz Version: 0.12a-5 I've not heard from the author wrt my query below. I'm filing this bug to make sure that this issue gets checked rather than forgotten. Thank you for your attention.
Ian. Mike Neuffer writes ("Re: lrzsz ? Re: forwarded message from CERT Bulletin"): ... > I'm not the author, but lrzsz is almost identical to the "normal" rzsz > implemetation the only difference is that it gives more status information. > The diff itself is rather small. ------- start of forwarded message (RFC 934 encapsulation) ------- In-Reply-To: <[EMAIL PROTECTED]> References: <[EMAIL PROTECTED]> To: Debian private list <[EMAIL PROTECTED]> Subject: lrzsz ? Re: forwarded message from CERT Bulletin CERT write: > Topic: "Trojan Horse" vulnerability via rz program ... > All existing versions of the rz program (a program for receiving > files over serial lines using the Z-Modem protocol) are equipped > with a feature that allows the sender of a file to request the > execution of arbitrary commands on the receiver's side. The user > using rz does not have any control over this feature. > > The workaround is to have rz never execute any command, and > always pretend a successful execution. The version we distribute is called `lrzsz', and I suspect it is a different version. Nevertheless I'd appreciate it if the author could confirm that the command execution feature is disabled. Ian. ------- end ------- ------- start of forwarded message (RFC 934 encapsulation) ------- Article: 124 of comp.security.announce Path: lyra.csx.cam.ac.uk!warwick!usenet.eel.ufl.edu!spool.mu.edu!news.sgi.com!enews.sgi.com!lll-winken.llnl.gov!uwm.edu!math.ohio-state.edu!news.cis.ohio-state.edu!nntp.sei.cmu.edu!news.sei.cmu.edu!cert-advisory Newsgroups: comp.security.announce Organization: CERT(sm) Coordination Center - +1 412-268-7090 Lines: 206 Approved: cert-advisory@cert.org Distribution: world Message-ID: <[EMAIL PROTECTED]> Reply-To: [EMAIL PROTECTED] NNTP-Posting-Host: why.cert.org Keywords: security CERT Originator: cert-advisory@cert.org Originator: [EMAIL PROTECTED] From: CERT Bulletin <cert-advisory@cert.org> Subject: CERT Vendor-Initiated Bulletin VB-96.12 - FreeBSD Date: 30 Jul 1996 19:22:18 GMT - -----BEGIN PGP SIGNED MESSAGE----- ============================================================================= CERT(sm) Vendor-Initiated Bulletin VB-96.12 July 30, 1996 Topic: "Trojan Horse" vulnerability via rz program Source: FreeBSD, Inc. To aid in the wide distribution of essential security information, the CERT Coordination Center is forwarding the following information from FreeBSD, Inc. FreeBSD, Inc. urges you to act on this information as soon as possible. FreeBSD, Inc. contact information is included in the forwarded text below; please contact them if you have any questions or need further information. =======================FORWARDED TEXT STARTS HERE============================ ============================================================================= FreeBSD-SA-96:17 Security Advisory Revised: Tue Jul 16 21:44:54 PDT 1996 FreeBSD, Inc. Topic: "Trojan Horse" vulnerability via rz program Category: ports Module: rzsz Announced: 1996-07-16 Affects: All FreeBSD ports collections released before 2.1.5-RELEASE Corrected: ports collection as of 1996-07-06 Source: rzsz shareware package FreeBSD only: no Patches: ftp://freebsd.org/pub/CERT/patches/SA-96:17/ ============================================================================= I. Background All existing versions of the rz program (a program for receiving files over serial lines using the Z-Modem protocol) are equipped with a feature that allows the sender of a file to request the execution of arbitrary commands on the receiver's side. The user using rz does not have any control over this feature. The workaround is to have rz never execute any command, and always pretend a successful execution. All FreeBSD users are encouraged to use the workaround provided. Since the intent of the Z-Modem protocol is to provide a reliable connection between systems of a vastly different architecture, the execution of local commands at request of the sending side cannot even be considered a useful feature at all. II. Problem Description The Z-Modem protocol specifies a mechanism which allows the transmitter of a file to execute an arbitrary command string as part of the file transfer. This is typically used to rename files or eliminate temporary files. A malicious "trusted" sender could send down a command that could damage a user's environment. III. Impact The rzsz package is an optional port that made be installed on some FreeBSD systems. This program is not installed by default. Systems without this program are not vulnerable. rz allows "Trojan Horse" type attacks against unsuspecting users. Since the rz executable does not run with special privileges, the vulnerability is limited to changes in the operating environment that the user could willingly perform. This vulnerability is a fundamental flaw in the Z-Modem protocol. Other operating systems and other implementations of the Z-Modem protocol may also suffer similar vulnerabilities. IV. Workaround Disable the rz program. If it has been installed, it would typically be found in /usr/local/bin. # chmod 000 /usr/local/bin/rz # ls -l /usr/local/bin/rz ---------- 1 root wheel 23203 Mar 4 23:12 /usr/local/bin/rz V. Solution(s) This feature is a relatively unknown part of the Z-Modem protocol. It is not critical to file transfers in general. The safest approach is to disable this feature in the receiving program. Any rzsz port that is obtained from the official ports collection after 1996-07-06 includes the following patch to disable this feature. This patch applies to rzsz v3.42, if you have an earlier version of the rzsz sources, please upgrade to the latest version first. *** rz.c.orig Sat Jul 6 17:34:26 1996 --- rz.c Sat Jul 6 17:44:52 1996 *************** *** 1020,1039 **** --- 1020,1045 ---- case ZCOMMAND: cmdzack1flg = Rxhdr[ZF0]; if (zrdata(secbuf, 1024) == GOTCRCW) { + #ifdef BIG_SECURITY_HOLE void exec2(); if (cmdzack1flg & ZCACK1) stohdr(0L); else stohdr((long)sys2(secbuf)); + #else + stohdr(0L); + #endif purgeline(); /* dump impatient questions */ do { zshhdr(4,ZCOMPL, Txhdr); } while (++errors<20 && zgethdr(Rxhdr) != ZFIN); ackbibi(); + #ifdef BIG_SECURITY_HOLE if (cmdzack1flg & ZCACK1) exec2(secbuf); + #endif return ZCOMPL; } zshhdr(4,ZNAK, Txhdr); goto again; ============================================================================= FreeBSD, Inc. Web Site: http://www.freebsd.org/ Confidential contacts: [EMAIL PROTECTED] PGP Key: ftp://freebsd.org/pub/CERT/public_key.asc Security notifications: [EMAIL PROTECTED] Security public discussion: [EMAIL PROTECTED] Notice: Any patches in this document may not apply cleanly due to modifications caused by digital signature or mailer software. Please reference the URL listed at the top of this document for original copies of all patches if necessary. ============================================================================= ========================FORWARDED TEXT ENDS HERE============================= 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 CERT Contact Information - - ------------------------ Email [EMAIL PROTECTED] 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 from[-1z 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 [EMAIL PROTECTED] CERT is a service mark of Carnegie Mellon University. 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