[V4] [RFC] Adding a SECURITY policy for GDB

[Andrew Burgess <aburgess@redhat.com>]

I realise I didn't tag my last update as V4.

I wonder if anyone has any thoughts on this latest iteration.

Andrew Burgess <aburgess@redhat.com> writes:

> Thank you all for the continued feedback.
>
> In V4 I have:
>
>   - Reordered some of the text.  As I was adding/changing words I felt
>     the old order didn't make as much sense, so some of the paragraphs
>     have been shuffled around a little,
>
>   - Added some text about per-project/per-program configuration files
>     not being auto-loaded unless the user specifically allows them, and
>     mentioned that a bug which allowed such auto-loading without a user
>     command would be a security issues,
>
>   - Added some words to try and reflect the (current) reality which is
>     that the ELF/DWARF loaders are known/likely to contain bugs when
>     confronted with malformed input, which could result in undefined
>     behaviour, which could be a security issue.  This effectively means
>     that, though we'd like to say it is safe to examine an untrusted
>     binary (so long as you don't execute it), in reality, it's not
>     really safe (currently) to do such a thing.
>
>     In some ways this is a return to the position from V1, against which
>     there was some push back.  However, the new text is slightly
>     different.  While V1 basically said "it's never safe to touch an
>     untrusted binary with GDB (outside of a sandboxed environment)", the
>     new text is trying to say "we'd like it to be safe to examine (but
>     not run) and untrusted binary, but we're not there yet".
>
>     This security document shouldn't be "final for all time", it should
>     be a living document, just like every other part of GDB.  Hopefully,
>     in time, we might one day reach a position where we feel we can say
>     not only that we'd like such a use of GDB to be secure, but that it
>     actually _is_ secure (to the best of our knowledge).
>
> All feedback welcome.
>
> Thanks,
> Andrew

---

 GNU Debugger Security Policy
 ============================

 Introduction
 ------------

   The GNU Debugger (GDB) is a tool for diagnosing issues "inside"
   another program.  This can be done by controlling the execution of
   the program being debugged and allowing the user to inspect and
   modify the state of the running program.  Or GDB can be used to
   analyse the program or a core file generated from the program
   without needing to execute the program.

   The program being debugged may be local i.e. on the system on which
   GDB runs or remote, on a different system.

 Policy Objectives
 -----------------

   The objective of this policy is define what the GDB project
   considers a security bug and what is a non-security bug, and how
   bugs can be reported.

   Additionally this policy discusses areas of GDB in which there are
   known bugs, how these might lead to security issues, and how this
   risk can be mitigated.

 Scope Of This Policy
 --------------------

   This policy covers all currently supported versions of GDB as
   released from the official GDB website and covers gdb, gdbserver, as
   well as gcore and gdb-add-index, which are packaged with each GDB
   release.  The official GDB website can be found here:

     https://sourceware.org/gdb/

   Remote debugging uses GDB to connect to a remote target.  GDB sends
   commands to the remote target which then controls the process being
   debugged.  The GDB project provides one remote target, gdbserver,
   which is included with official GDB releases.  Bugs within gdbserver
   are in scope for this policy.

   Other projects also implement remote targets to which GDB can
   connect.  Any bugs in these remote targets are out of scope for this
   policy and should be reported to the relevant project.  However, any
   bugs in GDB caused by a misbehaving remote target, even when that
   target is not gdbserver, are in scope for this policy.

 What Is A Security Bug?
 -----------------------

   Any bugs in GDB or gdbserver that result in an unexpected crossing
   of a privilege boundary are considered security bugs.  Some examples
   of crossing a privilege boundary include: being able to execute code
   as an arbitrarily different user, or accessing resources
   (e.g. files, sockets, etc) for which the original user would not
   normally have access.

   Any bugs in GDB that result in execution of the program being
   debugged without the user issuing a GDB command triggering execution
   (either from the GDB command line, a GDB configuration file, or from
   the GDB prompt) are considered security bugs.

   GDB will check for and load multiple configuration files.  When
   initially started GDB can load user and system specific
   configuration files, this is done unconditionally as it is assumed
   these files are under control of the user and are always safe to
   load.

   GDB can also load per-project and per-program configuration files,
   this is done when a program to debug is loaded into GDB.  These
   configuration files will only be loaded if the use has given GDB
   permission to load these files.  Any bug in GDB which allows
   per-project or per-program configuration files to be loaded without
   permission having been granted by the user is considered a security
   bug.

   When gdbserver is started, if it is passed a program on its command
   line then that program will be started, but paused before executing
   its first instruction.

   Any bug in gdbserver which results in further execution of the
   program being debugged without GDB first connecting to the target
   and sending a command that is intended to trigger execution is a
   security bug in gdbserver.

   Any bug in GDB or gdbserver that can trigger arbitrary code
   execution without the program being debugged having been executed by
   a user command, is considered a security bug, e.g. if loading a
   program into GDB could trigger arbitrary code execution, then this
   is a security issue.

   The additional tools gcore and gdb-add-index are scripts that wrap
   around GDB.  Any issue in these tools that meet the above
   definitions of a security bug, are considered a security bug.

 What Is Not A Security Bug
 --------------------------

   In the context of local debugging, when GDB is used to execute a
   program, the program runs with the same privileges as GDB itself.

   Any issues that arise from running an untrusted program outside of a
   secure environment are not security bugs in GDB.  Any issues that
   arise from running an untrusted program through GDB inside a secure
   environment are only security bugs if GDB is required in order to
   trigger the issue.

   It is possible for a program to detect when it is run under GDB and
   to change its behavior so that unwanted behavior may only appear
   when a program is run under GDB.  Any issues that arise due to an
   untrusted program detecting GDB and changing its behaviour are not
   security issues in GDB unless the issue also meet some other
   definition of a security bug.

   In the context of remote debugging, the program being debugged is
   run with the same privileges as gdbserver.  As with GDB in the local
   debugging case, any issues that arise from running an untrusted
   program outside of a secure environment are not security bugs in
   gdbserver.

   The connection between GDB and a remote target is not protected by
   either authentication or encryption.  Connecting to a remote target
   allows for arbitrary code execution on the remote system with the
   same privileges as the remote user, and any resource that the remote
   user can access can be read by GDB, and downloaded to the local
   machine on which GDB is running.  As such, users need to take
   independent measures to secure the connection between GDB and the
   remote target.

   Any issues that arise due to a failure to protect the connection
   between GDB and a remote target are not security bugs in either GDB
   or gdbserver.

 Security Realities Of The GDB Project
 -------------------------------------

   Within this section, references to GDB should be read as meaning
   GDB, gdbserver, gcore, or gdb-add-index, unless specifically stated
   otherwise.

   The most common use case for GDB is a developer trying to resolve
   issues within a program that they have either written themselves, or
   within a program that they trust not to be malicious.  In this
   situation we would say GDB is being used to debug trusted code.
   There is no greater security risk from running the program to debug
   through GDB than there is running the program directly.  Additional
   process isolation for the GDB process is only needed if additional
   isolation would have been applied anyway when running the program to
   debug.

   In some cases a developer may be given a program from an untrusted
   source and be asked to debug an issue.  In this situation we would
   say GDB is being used to debug untrusted code.  In this case the
   user should take all the precautions when running GDB that they
   would normally take when running an untrusted program outside of
   GDB, e.g. running within a secure, sandboxed environment.

   When using GDB to examine, but not execute, an untrusted program
   (with gdbserver, the program will be started, but paused at the
   first instruction and not run further), there should be no security
   risks, however the GDB maintainers don't currently believe that GDB
   or gdbserver is reliable enough to ensure that there are no security
   risks.

   There are known bugs in GDB related to loading malformed executables
   and parsing the debug information, a consequence of these bugs is
   that a malicious program could trigger undefined behaviour in GDB,
   which could be used to trigger arbitrary code execution.

   Given these risks, the advice of the GDB project is that, when using
   GDB with an untrusted binary, always do so in a secure, sandboxed
   environment.

   As there are already known bugs in GDB relating to undefined
   behaviour triggered from malformed programs, further bugs in this
   area should still be reported, but are unlikely to be given high
   priority.  Bugs in GDB that are triggered by well-formed programs
   should also be reported, and are likely to be treated as higher
   priority as these are more likely to impact normal use of GDB.

   When using GDB and gdbserver to perform remote debug, the connection
   between the two components is by design insecure.  It is up to the
   user to protect this connection, for example, by only starting
   gdbserver within a secure network.

 Reporting Non-Security Bugs
 ---------------------------

   NOTE: All bugs reported in the GDB Bugzilla are public.

   Non-security bugs, as well as any security bugs that pose limited
   risk to users should be reported in GDB's bugzilla system.  Bugs
   reported in this way will be public.  The bugzilla system can be
   found here:

     https://sourceware.org/bugzilla/

 Reporting Security Bugs
 -----------------------

   In order to report a private security bug that is not immediately
   made public, please contact one of the downstream distributions with
   security teams.  The following teams have volunteered to handle such
   bugs:

      Red Hat: secalert@redhat.com
      SUSE:    security@suse.de

   Please report the bug to just one of these teams.  It will be shared
   with other teams as necessary.

   The team contacted will take care of details such as vulnerability
   rating and CVE assignment (http://cve.mitre.org/about/).  It is
   likely that the team will ask to file a public bug because the issue
   is sufficiently minor and does not warrant keeping details of the
   bug private.