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** Tags added: patch

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https://bugs.launchpad.net/bugs/1573594

Title:
  Missing null termination in PROTOCOL_BINARY_CMD_SASL_LIST_MECHS
  response handling

Status in libmemcached:
  New
Status in libmemcached package in Ubuntu:
  In Progress
Status in libmemcached source package in Trusty:
  In Progress
Status in libmemcached source package in Xenial:
  In Progress
Status in libmemcached source package in Bionic:
  In Progress
Status in libmemcached source package in Cosmic:
  In Progress
Status in libmemcached source package in Disco:
  In Progress

Bug description:
  [Impact]

  When connecting to a server using SASL,
  memcached_sasl_authenticate_connection() reads the list of supported
  mechanisms [1] from the server via the command
  PROTOCOL_BINARY_CMD_SASL_LIST_MECHS. The server's response is a string
  containing supported authentication mechanisms, which gets stored into
  the (uninitialized) destination buffer without null termination [2].

  The buffer then gets passed to sasl_client_start [3] which treats it
  as a null-terminated string [4], reading uninitialised bytes in the
  buffer.

  As the buffer lives on the stack, an attacker that can put strings on
  the stack before the connection gets made, might be able to tamper
  with the authentication.

  [1] libmemcached/sasl.cc:174
  [2] libmemcached/response.cc:619
  [1] libmemcached/sasl.cc:231
  [3] http://linux.die.net/man/3/sasl_client_start

  
  [Test Case]

  There is no known reliable reproducer.

  
  [Regression Potential]

  This fix initialises the buffer to 0.
  Any potential regression may include failure of the authentication when using SASL.

  
  [Other Info]

  This bug affects trusty and later.

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