IP: HOT OFF THE PRESS -- DO READ Comments on the Carnivore System Technical Review

[Dave Farber <farber () cis upenn edu>]

              Comments on the Carnivore System Technical Review

                               Steven M Bellovin
                               AT&T Laboratories
                             smb () research att com

                                  Matt Blaze
                               AT&T Laboratories
                             mab () research att com

                                 David Farber
                          University of Pennsylvania
                             farber () cis upenn edu

                                 Peter Neumann
                               SRI International
                             neumann () csl sri com

                                Eugene Spafford
                           Purdue University CERIAS
                            spaf () cerias purdue edu

                               3 December 2000

I Introduction

In September, 2000, we were asked by the Chief Scientist of the US
Department of Justice to identify technical issues with the FBI's Carnivore
Internet wiretap system that should be addressed by an independent review.
On October 2, we met with Justice officials in Washington, DC, where we
identified various areas of concern and issues that we believed must be
addressed by any meaningful review process.

The contractor chosen by the Government to conduct this review, IIT Research
Institute, recently released a draft report of its findings ("Independent
Technical Review of the Carnivore System", dated 17 November 2000). We have
studied that report and we continue to have serious concerns relating to the
Carnivore system.

Although the IITRI study appears to represent a good-faith effort at
independent review, the limited nature of the analysis described in the
draft report simply cannot support a conclusion that Carnivore is correct,
safe, or always consistent with legal limitations. Those who are concerned
that the system produces correct evidence, represents no threat to the
networks on which it is installed, or complies with the scope of court
orders should not take much comfort from the analysis described in the
report or its conclusions.

We are especially concerned with several serious limitations of the analysis
as presented:

    * There is a lack of analysis of operational and "systems" issues,
      including interactions between the Carnivore code and its host
      environment and operating system. Many potential security flaws and
      collection errors are likely to be found in this area.

    * There is no evidence of a systematic search for bugs, not even such
      common (and serious) errors as string buffer overflows or URL or header
      parsing problems, although these are listed as potential issues.

    * The exclusion from analysis or testing of RADIUS is a very serious
      omission; RADIUS is especially difficult to interpret in a
      vendor-independent fashion, and has been cited as a source of Carnivore
      problems in media reports.

    * There is inadequate discussion of audit and logging (both of logs
      maintained by Carnivore itself and of logs maintained by the host
      operating system and supporting tools). This is especially serious in
      light of the use of "PC Anywhere" and "Administrator" logins for remote
      access, which permits any files to be uploaded or changed, including
      the logs and audit trails.

II Conclusions and Recommendations

Unfortunately, serious technical questions remain about the ability of
Carnivore to satisfy its requirements for security, safety, and soundness.
While the IITRI report does represent a good starting point for answering
these questions, we were disappointed that more attention was not paid to
operational and "systems" issues. It is simply not possible to draw
meaningful conclusions about isolated pieces of software without also
considering the computing, networking, and user environment under which they
are running. These and other areas must be examined further if the legal
community, ISPs, and the public are to have confidence that Carnivore works
as it is supposed to.

We also urge that the report's recommendations with regard to logging and
audit be considered carefully and made a high priority. The Carnivore system
does not produce meaningful or secure audit trails. This is obviously a very
serious deficiency.

We applaud the DoJ and IITRI for their openness in the Carnivore review
process, especially in light of the time constraints under which the review
was conducted and the extraordinary sensitivity of critical law-enforcement
surveillance technology. Nonetheless, we must emphasize that no single
review can ever capture every potential problem with critical software of
this complexity, especially when it must be run under a wide range of
operational environments. Furthermore, as the software is enhanced and the
environment under which it runs evolves, existing reviews may well be
rendered obsolete. As such, the Department of Justice must consider an
on-going process to maintain confidence in the system. One such approach is
to publish the Carnivore source code for public review. Although an
extraordinary step, we urge the DoJ to consider it seriously.

III Itemized Comments

Following is a list of comments keyed to the roman page numbers or symbolic
section numbers in the draft report.

p. xiii
      There is a statement that Carnivore is not powerful enough to capture
      everything, that unless the filter is configured correctly, it will not
      accurately collect data. This implies that it might not keep up with
      heavy load as part of a lawful intercept. As such, this issue should be
      explored to ensure Carnivore behaves correctly under heavy load.

ES.4
      The user must be logged in as Administrator. This is bad, because flaws
      in the code can easily lead to system penetrations and violations of
      least privilege.

      Putting more and more into the driver is a poor way to produce a robust
      system. It requires too much privileged code.

      There are two typos: DLL stands for "dynamic link library." The correct
      brand name of the removable disk drive is "Jaz" and not "Jazz" disk.

ES.5
      The draft says that "Carnivore represents technology that can be more
      effective in protecting privacy and enabling lawful surveillance than
      can alternatives." What alternatives? The scope of this statement is
      undefined.

ES.6
      A "CRC" should not be used. Instead, a cryptographically strong "MAC"
      (message authentication code) or (at the least) a cryptographic
      checksum such as SHA-1 should be used. (Note: "CRC" -- "cyclic
      redundancy check" -- refers to a particular mathematical algorithm; it
      is simply one form of checksum.)

1.1.1
      There is mention in point 17 about possible string buffer overflows in
      Carnivore or related tools. But there is no further discussion in the
      report. This is a very serious omission in the report; buffer overflows
      are among the most common causes of security weaknesses in network
      software.

      Clearly, the IITRI team could not do a thorough search for buffer
      overflows in the allocated time. But some analysis of the possible
      consequences of an overflow -- in Carnivore, CoolMiner, Packeteer, or
      wherever -- should be feasible.

      More generally, are there sanity checks on collected data?

      In general, there should have been a much more thorough search for
      bugs. The problems with the analysis programs should have been found in
      earlier testing by the FBI.

3.2.3
      Why is the second minimization done by the case agent? If impermissible
      data is collected by Carnivore, the case agent can learn its contents
      before deleting it. This seems to violate the separation policy
      otherwise used.

3.4.3
      PCAnywhere is far too powerful for this purpose. Any files can be
      changed or modified, with no auditing. A less general mechanism that
      provides suitable logging and that does not permit remote modification
      of log files would be far better.

3.4.4
      Apart from the issue of a compiled-in password, standard practice calls
      for such passwords to be one-way hashes, rather than plaintext.

3.4.4.1.2
      What protections are there against forged RADIUS or DHCP packets? What
      about forged addresses in general? Is the ISP required to do ingress
      filtering?

3.5.1
      The note that "Carnivore is not intended to ... collect all packets" is
      wrong; that's a function that (as noted elsewhere) is present simply
      because of its behavior with no filters.

3.5.3
      Table 3-1 is unclear on what happens if the strings appear in the
      middle of a packet, or if the string is split across two packets. See,
      for example, RFC 2920, for one way in which this can happen for e-mail.

      The handling of fragments is frequently problematic and should be
      addressed further.

3.6.10
      DCHP can key on host name, not only MAC address.

4.1
      The Windows NT configuration is quite crucial. This must be evaluated.
      Is there an IP stack? Can incoming packets crash or compromise the host
      environment even before the packets get to Carnivore? What is done for
      NT installation and configuration management? All conclusions depend on
      "correct configuration"; how likely is that in practice?

      RADIUS is not similar to DHCP, and in fact poses a large number of
      operational issues. In particular, there are numerous
      non-interoperable, vendor-specific extensions. The crash in the
      Earthlink case is rumored to stem from limitations in Carnivore's
      RADIUS-handling code (thus forcing the ISP to fall back to less-stable
      code that implemented a desired profile of RADIUS); failure to evaluate
      the Carnivore implementation is not acceptable.

4.2.1
      The ISP has no way to verify that the settings have been correctly
      entered. Indeed, this seems to be a FBI requirement in some cases --
      they report that in some cases the name of the person being intercepted
      is deliberately kept hidden from the ISP. (This suggests that Carnivore
      provides functionality to the FBI in excess of what can be obtained by
      cloning the target's e-mail account.) This contradicts the statement
      that Carnivore is used only when an ISP cannot provide the relevant
      data.

4.2.2
      The report suggests that judicial oversight is the ultimate check on
      abuse. Given examples of the failure of such processes -- notably the
      recent wiretap fiasco in Los Angeles -- it is difficult to be
      completely reassured.

      This will become more of an issue if and when Carnivore versions are
      made available to more police agencies around the country.

4.2.3
      Most protocol messages are not guaranteed to start on TCP packet
      boundaries.

4.2.4
      In general, we agree with the report that much more attention needs to
      be paid to audit trails.

      Carnivore seems to allow use of keyword searching on all IP traffic on
      the subnet (no filtering to specific IP addresses). We would be
      interested to hear opinions on whether this capability is authorized by
      wiretap law.

4.2.6
      We agree that the lack of a formal development environment, including
      formal and auditable change management to the source code, is crucial.

4.2.8
      It is not legal to look at mail headers with a pen register warrant,
      because it can disclose correspondence between two or more parties who
      are not subjects of the court order.

      What are the consequences of missed or out-of-order packets? As
      Carnivore is not in-line in the protocol, it is quite difficult and not
      always possible to detect missed or out-of-order packets.

      The report states that under-collection is never a risk. This isn't
      true; missed RADIUS packets, missing exculpatory e-mail messages, etc.,
      can have a large impact. How can an agent determine if traffic was
      missed or lost?

      There seem to be a number of cases of potential over-collection in pen
      mode. It captures entire IP headers for some protocols. It captures the
      entire packet if it contains an SMTP MAIL FROM: command, even though
      the rest of the packet might contain content (e.g., the body of an
      e-mail).

      In pen-mode, it captures and displays lengths of various
      communications. One concern is that this allows traffic analysis -- for
      instance, in the case of a user visiting a web site, knowing the length
      of the objects returned can often be used to identify which web page he
      was visiting (at least for static HTML content), and this is clearly
      not authorized in pen mode. (Images, in particular, are quite
      distinctive that way.)

      It also collects and displays lengths of, e.g., Subject: lines in pen
      mode.

4.3.2
      There was very little analysis of different ISP configurations. What
      versions of DHCP or RADIUS is Carnivore compatible with? What DHCP
      options does it understand? How likely are the operational changes
      which may be required? Again, the Earthlink case is a warning.

5.2
      We very much agree with the suggestion that separate versions be used
      for pen-register versus full-content intercepts. Usability in general
      is a concern, especially given that the default is to collect
      everything; configuration is a matter of telling Carnivore to exclude
      certain things.

5.5
      It would also seem to be a good idea to capture the entire
      configuration of the machine after it is used; perhaps they could use a
      removable hard disk (as their only permanent storage, so that all
      software, everything would live on it), and after finishing an
      interception, put the the removable disk under seal.

5.9
      "Once Packeteer and CoolMiner have had all the software bugs fixed,
      ..." The possibility of removing all bugs is a bad thing to assume. On
      the other hand, this software is being used now. It would be preferable
      to give defense attorneys whatever version is being used, even a buggy
      one, as that is the the tool used in the cases against their clients.



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