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NetBSD Security Advisory 2016-001: Multiple vulnerabilities in ntp daemon
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NetBSD Security Advisory 2016-001
Topic: Multiple vulnerabilities in ntp daemon
Version: NetBSD-current: source prior to Fri, Oct 23 2015
NetBSD 7.0: affected
NetBSD 6.1 - 6.1.5: affected
NetBSD 6.0 - 6.0.6: affected
Severity: Local DoS / Kernel execution redirection
Fixed: NetBSD-current: Fri, Oct 23 2015
NetBSD-7-0 branch: Sat, Nov 7 2015
NetBSD-6-1 branch: Sat, Nov 7 2015
NetBSD-6-0 branch: Sat, Nov 7 2015
NetBSD-6 branch: Sat, Nov 7 2015
Teeny versions released later than the fix date will contain the fix.
Please note that NetBSD releases prior to 6.0 are no longer supported.
It is recommended that all users upgrade to a supported release.
Several bugs were fixed in the ntp-4.8.4p4 release that affect the
daemon operation and can be remotely exploited:
- crash the daemon
- perform code injection
- change time
- overwrite files
- consume excessive CPU and/or disk space
1. Remote Configuration Attacks
If ntpd(8) is configured to allow remote configuration, and if
the (possibly spoofed) source IP address is allowed to send
remote configuration requests, and if the attacker knows the
remote configuration password or if ntpd(8) was configured to
disable authentication, then an attacker can can send a set of
packets to ntpd(8) that may cause it to:
- Memory corruption, with the hypothetical possibility of
a code injection.
- Overwrite files.
- Crash and/or create a potentially huge log file.
Specifically, the attacker could enable extended
logging, point the key file at the log file, and cause
what amounts to an infinite loop.
- Overwrite other files. In particular possible for an
attacker to use the "pidfile" or "driftfile" directives
to potentially overwrite other files.
The default configuration of ntpd(8) within NetBSD does not
allow remote configuration.
2. Autokey issues
If ntpd(8) is configured to use autokey, then an attacker can
send packets to ntpd that will, after several days of ongoing
attack, cause it to run out of memory.
The fix for CVE-2014-9750 was incomplete in that there were
certain code paths where a packet with particular autokey
operations that contained malicious data was not always being
completely validated. Receipt of these packets can cause ntpd
[CVE-2015-7691, CVE-2015-7692, CVE-2015-7702].
The default configuration of ntpd(8) within NetBSD does not use
3. Crypto-NAK packets
Crypto-NAK packets can be used to cause ntpd(8) to accept time
from an unauthenticated ephemeral symmetric peer by bypassing
the authentication required to mobilize peer associations.
4. Crafted mode 6 and 7 packets
If ntpd(8) is fed a crafted mode 6 or mode 7 packet containing
an unusually long data value where a network address is expected,
the decodenetnum() function will abort with an assertion failure
instead of simply returning a failure condition.
If ntpd(8) is configured to enable mode 7 packets, and if the
use of mode 7 packets is not properly protected through the use
of the available mode 7 authentication and restriction mechanisms,
and if the (possibly spoofed) source IP address is allowed to
send mode 7 queries, then an attacker can send a crafted packet
to ntpd that will cause it to crash.
The default configuration of ntpd(8) within NetBSD does not
allow mode 7 packets.
5. Custom refclock driver incomplete data validation
A negative value for the datalen parameter will overflow a data
buffer. The NTF ntpd(8) driver implementation always sets this
value to 0 and are therefore not vulnerable to this weakness.
If the system runs a custom refclock driver in ntpd(8) and that
driver supplies a negative value for datalen (no custom driver
of even minimal competence would do this), then ntpd(8) would
overflow the data buffer. It is even hypothetically possible in
this case that instead of simply crashing ntpd(8), the attacker
could effect a code injection attack.
6. ntpq(8) potential memory corruption
If an attacker can figure out the precise moment that ntpq(8)
is listening for data and the port number on which it is listening,
or if the attacker can provide a malicious instance ntpd(8) that
victims will connect to, then an attacker can send a set of
crafted mode 6 response packets that, if received by ntpq(8),
can cause ntpq(8) to crash.
7. Kiss Of Death packet issues
An ntpd(8) client that honors Kiss-of-Death responses will honor
Kiss-of-Death messages that have been forged by an attacker,
causing it to delay or stop querying its servers for time updates.
Also, an attacker can forge packets that claim to be from the
target and send them to servers often enough that a server that
implements Kiss-of-Death rate limiting will send the target
machine a Kiss-of-Death response to attempt to reduce the rate
of incoming packets, or it may also trigger a firewall block at
the server for packets from the target machine. For either of
these attacks to succeed, the attacker must know what servers
the target is communicating with. An attacker can be anywhere
on the Internet and can frequently learn the identity of the
time source of a target by sending the target a time query.
Solutions and Workarounds
- - Upgrade your system to a NetBSD release that contains that patches,
and restart your ntpd(8).
- - Limit access to only trusted hosts via a packet filter.
- - Compile and use the ntp package from pkgsrc
Thanks to the NTP developers for correcting these issues.
Matthew Van Gundy of Cisco ASIG for reporting CVE-2015-7871.
Yves Younan, Aleksander Nikolich of Cisco Talos for reporting
Yves Younan fo Cisco Talos for reporting CVE-2015-7849,
Aleksandar Nikolic of Cisco Talos for reporting CVE-2015-7848.
Tenable for reporting CVE-2015-7691, CVE-2015-7692,
Red Hat for reporting CVE-2015-7703.
Aanchal Malhotra, Isaac E. Cohen, Erik Brakke, Sharon Goldberg
of Boston University for reporting CVE-2015-7704,
John D "Doug" Birdwell of IDA.org for reporting CVE-2015-7855.
2016-04-16 Initial release
Advisories may be updated as new information becomes available.
The most recent version of this advisory (PGP signed) can be found at
Information about NetBSD and NetBSD security can be found at
http://www.NetBSD.org/ and http://www.NetBSD.org/Security/ .
Copyright 2015, The NetBSD Foundation, Inc. All Rights Reserved.
Redistribution permitted only in full, unmodified form.
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