The Risks Digest

The RISKS Digest

Forum on Risks to the Public in Computers and Related Systems

ACM Committee on Computers and Public Policy, Peter G. Neumann, moderator

Volume 17 Issue 93

Sunday 24 March 1996


o Java/Netscape security flaw
Ed Felten
o DTMF falsing by human speech & music
Tim Shepard
o More on list-bombing
Phil Agre
o CIAC Notes 96-01: Java/JavaScript; search security
John M. Fisher
o Info on RISKS (comp.risks)

Java/Netscape security flaw

Ed Felten <felten@CS.Princeton.EDU>
Fri, 22 Mar 1996 17:27:56 -0500

We have discovered another serious security flaw in the Java programming
language, which allows a malicious Java applet running under Netscape
Navigator (version 2.0 or 2.01) to execute arbitrary machine code.  We have
implemented an applet that exploits the flaw to remove a file.  Until a fix
is issued, Netscape users can protect themselves by disabling Java in the
Security Preferences dialog.

At present we are not releasing technical details about the flaw.  We will
announce the full details later; some of the details will also appear in our
upcoming paper in the proceedings of the IEEE Symposium on Security and
Privacy, to be published in May.  Our paper also contains an overall
analysis of Java's security.  For an advance copy of the paper, send mail to  The paper will be available in about a week.

[Note that the "security enhancements" announced by Netscape in version 2.01
of Netscape Navigator do not fix this flaw.  They fix two separate flaws found
last month, one found by us (RISKS-17.77) and independently by Steve Gibbons,
and the other found by David Hopwood (RISKS-17.83).]

For more information, see, or contact
Ed Felten at (609) 258-5906 or

Drew Dean, Ed Felten, Dan Wallach, Dept of Computer Science, Princeton Univ.

   [See the CIAC item at the end of this issue for some background
   on the earlier problems.  PGN]

DTMF falsing by human speech & music (Panero, RISKS-17.92)

Tim Shepard <>
Fri, 22 Mar 1996 23:46:34 -0500

In RISKS-17.92 Tony Panero (Hare Krsna chants ...) suggests that it is
difficult to avoid false detection of DTMF signals in human speech, but that
it was reasonable to do in-band signaling when tone dialing was originally
designed because dialing is not a context that typically includes speech.
Last year I stumbled across an interesting 1960 BSTJ article which appears
to be the original design document for what is now DTMF [1].  Guarding
against false detection of signalling tones in human speech and enabling use
of the signalling tones for end-to-end applications were the primary design
objectives. Here are a few passages from the introduction:

  "In recent years, customer signaling from a telephone set by means of
  pushbuttons has appeared increasingly promising. An early plan has been
  reported in which the operation of a pushbutton produces four effects: (a)
  the generation of a damped oscillatory wave at one of ten
  digit-identifying frequencies with the voice range; (b) the generation of
  a similar damped wave at one of eight party-identifying frequencies, also
  in the voice range; (c) a stepwise reduction of direct current drawn by
  the set and (d) the temporary disablement of the speech transmitter.
  Actions (c) and (d) provide protection against talk-off, i.e., false
  signaling due to speech or noise at the transmitter.

  "This plan contemplated only the transmission of information to the
  central office, but in the long run it would be advantageous to be able to
  signal "end-to-end," over any established connection that will transmit
  speech.  With this added objective several new considerations are
  introduced.  Clearly the signals should not contain an out-of-band
  component such as the dc step.  [...]

  "Voice-frequency signaling is, of course, already an established practice
  in the Bell System.  One example is multifrequency key pulsing (MFKP),
  which is widely used for toll signaling.  However, minimization of
  talk-off was not a factor in its development [...]

  "This paper describes an all-voice-frequency signaling system that
  provides substantial protection against talk-off.  [...]"

After the introduction the article proceeds through a discussion of the
design and describes the preferred way to build a detector (from filters,
hard limiters, and power detectors) to make it robust against talk-off.  The
essential part of the design is that to detect the presence of one of the
component tones, you filter out the signals in the other band while
carefully preserving as much energy as possible in other parts of the
spectrum.  You then pass this signal into a hard limiter whose output is
connected to a narrow selective filter for the tone of interest.  You then
detect the power in the signal coming out of the narrow filter.  Quoting

  "The selective circuitry that follows the limiter is designed to recognize
  a signal as bona fide only when it not only falls within a rather narrow
  passband, but also appears at an amplitude within about 2.5 db of the full
  output that the limiter is capable of delivering.  Thus when a burst of
  speech contains components at more than just the two signal frequencies,
  this fact is used to inhibit recognition of the signal frequencies in the
  burst. [...]"

Further discussion includes the selection of signaling frequencies, tone
power levels, and filter parameters to further reduce the likelihood of
false detection due to music or harmonic distortion of vowels in human
speech.  Each of these scenarios may lead to situations where a substantial
fraction of the energy in the signal is at the signalling frequencies.  By
providing just enough but not too much band-stop filtering, the detector can
be made less likely to false by not accepting tones when the relative power
levels aren't right, but still be able to cope with the amount of twist
typically found in the end-to-end frequency response of phone lines.

I do not doubt that many systems using DTMF signaling today are susceptible
to falsing.  I fear that the careful design that went into the DTMF system
specifically to enable the construction of DTMF detectors with good talk-off
resistance may have been forgotten.  IMHO this 1960 BSTJ article is a
must-read for anyone designing a DTMF detector, which over 30 years later is
likely to be a programmer writing (or cutting-and-pasting) DSP code.

[1] L. Schenker, "Pushbutton Calling with a Two-Group Voice-Frequency Code",
   _Bell System Technical Journal_, Jan 1960, Volume XXXIX, pages 235-255.

-Tim Shepard,

More on list-bombing (Re: RISKS-17.83)

Phil Agre <>
Fri, 22 Mar 1996 19:27:46 -0800 (PST)

I run a large mailing list, and every few weeks for the last several months
someone has complained that they were getting messages from me without
knowing why.  This was not just a matter of people getting forwarded
messages with misleading headers, since most of these people were in fact on
the mailing list.  Finally this week I sent a query on the subject to the
whole list.  Here is a summary of what I learned.

The Internet has indeed been suffering an epidemic of bogus mailing list
subscriptions, particularly over the last few weeks.  I have had reports
from numerous list maintainers of dozens of mysterious subscriptions suddenly
showing up on their lists, followed by confusion or acrimony.

Some instances are clearly malicious.  Numerous people have been involuntarily
subscribed to many mailing lists.  Celebrities who have been "list-bombed"
in this fashion include Rush Limbaugh (who reportedly discussed it on the
air) and Philip Elmer-Dewitt (who wrote about it for Time Magazine).  The
White House has been list-bombed too (and sent out a message to the effect
that list-bombing just hurts the interns who have to filter the stuff, not
the officials who presumably are the targets).  Two main motives have been
mentioned: political disagreement, often but not always with regard to
Internet issues like censorship (apparently this technique is being practiced
by dunderheads on both the left and the right); and spam (many spammers have
apparently gotten the list-bombing treatment).

List-bombing, however, does not seem to be the only phenomenon here.  Only
a few of the people who complained to me mentioned other mailing lists, and
I think that victims of list-bombing are much more likely to change to a new
account than to try unwinding all of their bogus subscriptions.  On my list I
speculated that a demon might be generating subscriptions on a random basis,
but nobody has reported any actual evidence for this.  At the same time, it
seems to be happening on too large a scale to have been done entirely by hand.

One particularly depressing point, mentioned by a few people, is that some
Web browsers make it very easy to forge mail by simply typing in the victim's
e-mail address when the browser starts up.  For example, the Web browsers on
the Macs in the undergraduate lab where I teach always start up by asking for
a name and e-mail address, and it doesn't take a rocket scientist to think
to type in someone else's information.

Several people explained ways, other than using Web browsers, to forge e-mail
headers.  I won't describe them; they are not very interesting.  I would like
to see pressure on authors of software that sends mail to remove features
that make it easy to forge headers.  We probably can't make it impossible,
but at least we can get rid of the amateurs.  I won't recount the even more
destructive (albeit more creative) possible uses of forged headers that some
people suggested.

That said, the real underlying problem is more basic: personal computers,
unlike mainframes, usually don't authenticate their users.  It is not at all
clear what to do about this.  As far as I can tell, the mail header standards
presuppose that there exists some determinate truth about what mail address
a message is "from", but this isn't the case (for example) on the publicly
available Apple Macintosh in the UCSD library on which I am now typing, which
can send e-mail but cannot receive it.  Another problem is that forgery of
mail headers has constructive uses, for example when mailing list maintainers
set the "From:" field to point at some alias other than their own personal
account in order to avoid getting swamped with e-mail related to the list.

Listserv has an option whereby the putative subscriber must reconfirm a
subscription by replying to an automatically generated message.  I believe
this feature originated to solve the more pervasive problem of e-mail messages
(subscription requests, for example) that are badly formed, or that come from
badly configured machines, or that otherwise cannot be replied to.  But it's
also a way to screen out forgeries, and as far as I can tell, all maintainers
of open mailing lists are going to have to shift to such a protocol soon.

The involuntary list subscriptions do not all result from hostile actions.
Some people attested cases in which a university or online service had
recycled an old user's name, giving it to someone else, so that the new user
got all of the old user's mailing list subscriptions.  One person speculated
that some of the mystery subscriptions may have come from friends subscribing
friends to the list without telling them.  Who knows.

It might be possible to track down the perpetrators by logging subscription
requests; if we were to save the complete header for each such request then
we might notice discrepancies and identify where the bogus messages were
from.  My own list, though, has about 3600 subscribers and a lot of turnover,
so the log file would grow quickly if it kept the complete headers.  Some of
the X.400 headers from Europe are pretty darn long.

It's worth pointing out, in case any list-bombers are reading this, that
even if your intended victim deserves it, list-bombing has nonetheless
been causing a lot of pain to innocent parties.  The most obvious are the
list-owners who have to deal with complaints, remove addresses, etc.  But the
other subscribers of the list must often wade through messages to the whole
list from victims, followed by other messages in reply that are probably not
relevant to the list's intended topic.

Finally, just in case any of the mystery subscriptions to my own list were
intended as revenge against me rather than against the involuntary subscriber,
at least a third of the involuntary subscribers say that they actually like
the list, and some of them have decided to stay.  My advice would be to grow
up and learn how to engage in real politics instead of this childish sabotage.

Phil Agre, UCSD

CIAC Notes 96-01: Java/JavaScript; search security

John M. Fisher <>
Mon, 18 Mar 1996 18:49:51 -0800 (PST)

CIAC is sending this addition of CIAC Notes to the CIAC Bulletins list
because of the high demand for information on Java and JavaScript
vulnerabilities.  [...]

CIAC Notes Number 96-01                                     March 18, 1996

This edition of CIAC NOTES includes:

    1) Java and JavaScript Vulnerabilities
    2) FIRST Conference Announcement [summarized for RISKS]
    3) Security and Web Search Engines
    4) Microsoft Word Macro Virus Update [Omitted for RISKS]

Please send your comments and feedback to

  $ Reference to any specific commercial product does not necessarily   $
  $ constitute or imply its endorsement, recommendation or favoring by  $
  $ CIAC, the University of California, or the United States Government.$

1)  Java and JavaScript Vulnerabilities, By John Fisher


Over the past several weeks, a variety of reports have surface regarding
security problems with Java and JavaScript. Java was developed by Sun
Microsystems Incorporated, and JavaScript was developed by Netscape
Incorporated. Java is available directly from Sun through the Java
Development Kit. Both Java and JavaScript are supported with Netscape
Navigator 2.0. Although similar in name, and in some ways similar in syntax,
these two languages are vastly different in their usage.  Accordingly, the
security problems that have been reported are completely separate as well.
This article maps out what problems have been reported and discusses the
availability of solutions.

Java applications communicate easily across a network environment,
particularly the Internet. Although not initially intended for this
environment, Java became a natural mechanism for enhancing the usability and
functionality of the World-Wide Web. With Java "applets," a Web site can
provide functionality for its visitors that is not available with HTML code.

Java can be used in a variety of different capacities. A standard Java
application can work stand-alone, providing functionality similar to other
programming languages (i.e., file input/output, graphical interfaces, etc).
When a Java application is made available on a Web site (via an HTML Web
page), it is in the form of a Java applet. An applet is given definite
restrictions on its capabilities. For example, a Java applet can not write
files to a Web visitor's local disk drive, or contact an Internet site
besides the server it was downloaded from. Java was supported with
Netscape's Navigator 2.0, released in February.

JavaScript is also supported in Navigator 2.0. Originally named LiveScript,
JavaScript code is placed directly in the text of an HTML document (as
opposed to being referenced in the HTML, similar to how an image would be
included, like Java does). For browsers that don't understand JavaScript,
JavaScript code simply seems to be a comment in the HTML code. For Navigator
2.0, a JavaScript program can provide additional functionality for the Web
page that can't be provided with just HTML. While JavaScript provides
increased functionality, it is syntactically simpler and less powerful than

Both Java and JavaScript have been developed with security in mind. Both
were developed with considerable emphasis on preventing a Web site from
gaining unintended access to a Web user's system or from performing actions
on behalf of the Web user without the user's knowledge.

Unfortunately, as is common with new technologies, unanticipated security
concerns have come to light. The next section addresses the latest security
concerns for Java and the section following addresses security issues for

Java Problems

The security problems reported about Java exist both in Netscape's Navigator
2.0 and in the Java Development Kit 1.0 from Sun Microsystems. Solutions to
both problems are provided below.

DNS Attack

In January, three students at Princeton University (Drew Dean, Ed Felten,
and Dan Wallach) discovered a way to use Java to exploit a well-known Domain
Name Service (DNS) vulnerability.

Note that this is not a vulnerability with Java, per se. It is really a
vulnerability with DNS that Java does not check for.

DNS servers provide a means for translating between host names and IP
addresses. For example, if a computer on the Internet were to initiate a
connection to the machine, the local DNS server for that
machine with resolve the host name as representing the IP address

Java applets running under Sun's appletviewer or Netscape's Navigator 2.0
are only allowed to connect the host from which they originated. To allow an
applet to connect to other hosts would be dangerous, as the applet would be
acting on behalf of the user who downloaded the applet. Imagine downloading
an applet from a Web site, only to find that the applet sent mail to another
system, acting as you. What's worse, without this restriction, a Java applet
would have all the access capabilities your machine does, including
accessing hosts behind a firewall.

The problem occurs because Java does not completely verify that the
information provided by the DNS server is accurate. Thus, if one can corrupt
the DNS server, it is possible to trick a Java applet into accessing an
arbitrary host. The potential for corrupting the information in DNS servers
is a known problem. See, for example, CIAC Bulletin G-14, Domain Name
Services Vulnerabilities.


In February, David Hopwood of Oxford University made public another
security problem with Java related to the loading of local class

Java provides a class loading capability which allows a Java applet to load
a class either from the host it originated from or from the user's local
system. Java applets residing on the user's local system are allowed special
capabilities such as reading and writing files or executing processes.
Either of these tasks can cause serious security problems if not used
properly. But, for large Java applets connecting to recognized hosts, the
additional functionality provided by placing class libraries on a local
system may be warranted.

Ordinarily, an applet is restricted to loading applets from the directories
specified in the environment variable CLASSPATH. However, Hopwood discovered
a way to load class libraries from any readable directory on a user's
system. This means that by placing a malicious class file and a dynamic
library on the user's system, an attacker can open that system to attack.

JavaScript Problems

Several different security problems have been identified with JavaScript as
well. Some of these vulnerabilities existed only in the public beta
distributions made available by Netscape Navigator 2.0. Others still were
present in the final release. The various problems reported include the

(1) Reading a user's URL history list and transmitting it to a remote site.
(2) Reading a user's disk cache (containing URLs recently acquired by
    the Web browser) and sending the information to the Web server.
(3) Stealing the e-mail address of the Web user and forging an e-mail
    message with it.
(4) Obtaining a recursive listing of local disk directories.
(5) Logging all URL accesses made by a Web browser and transmitting
    the information to a remote system.

Problems (1) and (2) were fixed in the final release of Netscape Navigator
2.0. The other problems were fixed in the latest release, described below.


Netscape solution

In late February, Netscape made a patch available to solve the DNS server

On March 14, Netscape released Navigator 2.01, which fixed all of the
vulnerabilities described above. It can be found at:

Sun Microsystems solution

On March 15, Sun released Java Development Kit 1.0.1, which fixed all
of the vulnerabilities described above. It can be found at:

  [Item 2 on the next FIRST conference deleted for space.
  See for info.  PGN]

3) Security and Web Search Engines, By John Fisher

A variety of very powerful search engines are available on the
Internet, including Netscape
(, Yahoo
(, Alta Vista (,
Lycos (, and others. These engines, known as "web
crawlers," provide a means for users to find URLs matching
keywords. Their databases are populated by gathering up all of the
available information provided by any Web server that can be
found. The Alta Vista database, for example, contains an index over 30
gigabytes in size.

But, perhaps, these search engines have become a little too powerful. Some
Web sites have provided a few too many links, including information related
to system configuration. For example, doing a search for keywords such as
"root", "daemon:", "passwd", etc, will return back a few stray /etc/passwd
or /etc/group files, located on systems that have very poor Web
configurations. This is a way to quickly find those Web sites that are not
maintained very well and are most vulnerable to attack.

So, the lesson here, if you maintain a Web site, be very sure of what
information you are making available. Make sure no URLs are available which
give configuration information about your system. With today's advanced
search engines, you may be opening yourself to unnecessary problems.

4) Microsoft Word Macro Virus Update, By Bill Orvis
   [See full issue for this item, omitted for RISKS.  PGN]

CIAC, the Computer Incident Advisory Capability, is the computer security
incident response team for the U.S. Department of Energy (DOE) and the
National Institutes of Health (NIH). CIAC is located at the Lawrence
Livermore National Laboratory in Livermore, California. CIAC is also a
founding member of FIRST, the Forum of Incident Response and Security Teams,
a global organization established to foster cooperation and coordination
among computer security teams worldwide.

CIAC services are available to DOE, DOE contractors, and the NIH. CIAC
can be contacted at:
    Voice:    +1 510-422-8193
    FAX:      +1 510-423-8002
    STU-III:  +1 510-423-2604

For emergencies and off-hour assistance, DOE, DOE contractor sites, and the
NIH may contact CIAC 24-hours a day. During off hours (5PM - 8AM PST), call
the CIAC voice number 510-422-8193 and leave a message, or call 800-759-7243
(800-SKY-PAGE) to send a Sky Page. CIAC has two Sky Page PIN numbers, the
primary PIN number, 8550070, is for the CIAC duty person, and the secondary
PIN number, 8550074 is for the CIAC Project Leader.

Previous CIAC notices, anti-virus software, and other information are
available from the CIAC Computer Security Archive.

   World Wide Web:
   Anonymous FTP: (
   Modem access:        +1 (510) 423-4753 (28.8K baud)
                        +1 (510) 423-3331 (28.8K baud)

CIAC has several self-subscribing mailing lists for electronic publications:
1. CIAC-BULLETIN for Advisories, highest priority - time critical
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2. CIAC-NOTES for Notes, a collection of computer security articles;
3. SPI-ANNOUNCE for official news about Security Profile Inspector
   (SPI) software updates, new features, distribution and
4. SPI-NOTES, for discussion of problems and solutions regarding the
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Our mailing lists are managed by a public domain software package
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subscribe (add yourself) to one of our mailing lists, send the
following request as the E-mail message body, substituting
valid information for LastName FirstName and PhoneNumber when sending

E-mail to
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You will receive an acknowledgment containing address, initial PIN, and
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Voice (510) 422-1463  Fax (510) 423-0913

  [Extensive background information and PGP enveloping removed for RISKS.
  See full issue. PGN]

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