Dropbear 2016.74, security updates

Matt Johnston matt at ucc.asn.au
Thu Jul 21 23:31:40 AWST 2016


Hi all,

Dropbear 2016.74 is released. This includes fixes for a few
security issues. Further details will be published by Beyond
Security in a week or so, I will update CVE numbers when available.

Downloads are at https://matt.ucc.asn.au/dropbear/dropbear.html

I strongly advise upgrading any systems where dbclient or
dropbearkey is used with arguments/input provided from external
sources, or systems where Unix usernames can be chosen
arbitrarily. The release also includes a fix for a
TCP forwarding issue that has affected quite a few people.

Cheers,
Matt

2016.74 - 21 July 2016

- Security: Message printout was vulnerable to format string injection.

  If specific usernames including "%" symbols can be created on a system
  (validated by getpwnam()) then an attacker could run arbitrary code as root
  when connecting to Dropbear server.

  A dbclient user who can control username or host arguments could potentially
  run arbitrary code as the dbclient user. This could be a problem if scripts
  or webpages pass untrusted input to the dbclient program.

- Security: dropbearconvert import of OpenSSH keys could run arbitrary code as
  the local dropbearconvert user when parsing malicious key files

- Security: dbclient could run arbitrary code as the local dbclient user if
  particular -m or -c arguments are provided. This could be an issue where
  dbclient is used in scripts.

- Security: dbclient or dropbear server could expose process memory to the
  running user if compiled with DEBUG_TRACE and running with -v

  The security issues were reported by an anonymous researcher working with
  Beyond Security's SecuriTeam Secure Disclosure www.beyondsecurity.com/ssd.html

- Fix port forwarding failure when connecting to domains that have both
  IPv4 and IPv6 addresses. The bug was introduced in 2015.68

- Fix 100% CPU use while waiting for rekey to complete. Thanks to Zhang Hui P
  for the patch


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