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[SECURITY] [DLA 193-1] chrony security update



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Package        : chrony
Version        : 1.24-3+squeeze2
CVE ID         : CVE-2015-1821 CVE-2015-1822 CVE-2015-1853
Debian Bug     : 782160

CVE-2015-1853:

  Protect authenticated symmetric NTP  associations against DoS attacks.

  An attacker knowing that NTP hosts A and B are peering with each other
  (symmetric association) can send a packet with random timestamps to host
  A with source address of B which will set the NTP state variables on A
  to the values sent by the attacker. Host A will then send on its next
  poll to B a packet with originate timestamp that doesn't match the
  transmit timestamp of B and the packet will be dropped. If the attacker
  does this periodically for both hosts, they won't be able to synchronize
  to each other. It is a denial-of-service attack.

  According to [1], NTP authentication is supposed to protect symmetric
  associations against this attack, but in the NTPv3 (RFC 1305) and NTPv4
  (RFC 5905) specifications the state variables are updated before the
  authentication check is performed, which means the association is
  vulnerable to the attack even when authentication is enabled.

  To fix this problem, save the originate and local timestamps only when
  the authentication check (test5) passed.

  [1] https://www.eecis.udel.edu/~mills/onwire.html

CVE-2015-1821:

  Fix access configuration with subnet size indivisible by 4.

  When NTP or cmdmon access was configured (from chrony.conf or via
  authenticated cmdmon) with a subnet size that is indivisible by 4 and
  an address that has nonzero bits in the 4-bit subnet remainder (e.g.
  192.168.15.0/22 or f000::/3), the new setting was written to an
  incorrect location, possibly outside the allocated array.

  An attacker that has the command key and is allowed to access cmdmon
  (only localhost is allowed by default) could exploit this to crash
  chronyd or possibly execute arbitrary code with the privileges of the
  chronyd process.

CVE-2015-1822:

  Fix initialization of reply slots for authenticated commands.

  When allocating memory to save unacknowledged replies to authenticated
  command requests, the last "next" pointer was not initialized to NULL.
  When all allocated reply slots were used, the next reply could be
  written to an invalid memory instead of allocating a new slot for it.

  An attacker that has the command key and is allowed to access cmdmon
  (only localhost is allowed by default) could exploit this to crash
  chronyd or possibly execute arbitrary code with the privileges of the
  chronyd process.
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