Security fix for CVE-2015-1853, CVE-2015-1821, CVE-2015-1822

Note that Tenable Network Security has extracted the preceding description block directly from the Fedora security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

Updated chrony packages that fix three security issues, several bugs, and add various enhancements are now available for Red Hat Enterprise Linux 7.

Red Hat Product Security has rated this update as having Moderate security impact. Common Vulnerability Scoring System (CVSS) base scores, which give detailed severity ratings, are available for each vulnerability from the CVE links in the References section.

The chrony suite, chronyd and chronyc, is an advanced implementation of the Network Time Protocol (NTP), specially designed to support systems with intermittent connections. It can synchronize the system clock with NTP servers, hardware reference clocks, and manual input.
It can also operate as an NTPv4 (RFC 5905) server or peer to provide a time service to other computers in the network.

An out-of-bounds write flaw was found in the way chrony stored certain addresses when configuring NTP or cmdmon access. An attacker that has the command key and is allowed to access cmdmon (only localhost is allowed by default) could use this flaw to crash chronyd or, possibly, execute arbitrary code with the privileges of the chronyd process.
(CVE-2015-1821)

An uninitialized pointer use flaw was found when allocating memory to save unacknowledged replies to authenticated command requests. An attacker that has the command key and is allowed to access cmdmon (only localhost is allowed by default) could use this flaw to crash chronyd or, possibly, execute arbitrary code with the privileges of the chronyd process. (CVE-2015-1822)

A denial of service flaw was found in the way chrony hosts that were peering with each other authenticated themselves before updating their internal state variables. An attacker could send packets to one peer host, which could cascade to other peers, and stop the synchronization process among the reached peers. (CVE-2015-1853)

These issues were discovered by Miroslav Lichvar of Red Hat.

The chrony packages have been upgraded to upstream version 2.1.1, which provides a number of bug fixes and enhancements over the previous version. Notable enhancements include :

* Updated to NTP version 4 (RFC 5905)

* Added pool directive to specify pool of NTP servers

* Added leapsecmode directive to select how to correct clock for leap second

* Added smoothtime directive to smooth served time and enable leap smear

* Added asynchronous name resolving with POSIX threads

* Ready for year 2036 (next NTP era)

* Improved clock control

* Networking code reworked to open separate client sockets for each NTP server

(BZ#1117882)

This update also fixes the following bug :

* The chronyd service previously assumed that network interfaces specified with the 'bindaddress' directive were ready when the service was started. This could cause chronyd to fail to bind an NTP server socket to the interface if the interface was not ready. With this update, chronyd uses the IP_FREEBIND socket option, enabling it to bind to an interface later, not only when the service starts.
(BZ#1169353)

In addition, this update adds the following enhancement :

* The chronyd service now supports four modes of handling leap seconds, configured using the 'leapsecmode' option. The clock can be either stepped by the kernel (the default 'system' mode), stepped by chronyd ('step' mode), slowly adjusted by slewing ('slew' mode), or the leap second can be ignored and corrected later in normal operation ('ignore' mode). If you select slewing, the correction will always start at 00:00:00 UTC and will be applied at a rate specified in the 'maxslewrate' option. (BZ#1206504)

All chrony users are advised to upgrade to these updated packages, which correct these issues and add these enhancements.

Miroslav Lichvar of Red Hat discovered multiple vulnerabilities in chrony, an alternative NTP client and server :

  - CVE-2015-1821     Using particular address/subnet pairs when configuring     access control would cause an invalid memory write. This     could allow attackers to cause a denial of service     (crash) or execute arbitrary code.

  - CVE-2015-1822     When allocating memory to save unacknowledged replies to     authenticated command requests, a pointer would be left     uninitialized, which could trigger an invalid memory     write. This could allow attackers to cause a denial of     service (crash) or execute arbitrary code.

  - CVE-2015-1853     When peering with other NTP hosts using authenticated     symmetric association, the internal state variables     would be updated before the MAC of the NTP messages was     validated. This could allow a remote attacker to cause a     denial of service by impeding synchronization between     NTP peers.

The remote Oracle Linux 7 host has a package installed that is affected by multiple vulnerabilities as referenced in the ELSA-2015-2241 advisory.

    - update to 2.1 (#1117882 #1169353 #1206504 #1209568 CVE-2015-1821       CVE-2015-1822 CVE-2015-1853)

Tenable has extracted the preceding description block directly from the Oracle Linux security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote host is affected by the vulnerability described in GLSA-201507-01 (chrony: Multiple vulnerabilities)

    Multiple vulnerabilities have been discovered in chrony. Please review       the CVE identifiers referenced below for details.
  Impact :

    A remote attacker can cause arbitrary remote code execution or Denial of       service condition.
  Workaround :

    There is no known workaround at this time.

Chrony News reports :

CVE-2015-1853: DoS attack on authenticated symmetric NTP associations

CVE-2015-1821: Heap-based buffer overflow in access configuration

CVE-2015-1822: Use of uninitialized pointer in command processing

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.

NOTE: Tenable Network Security has extracted the preceding description block directly from the DLA security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

An out-of-bounds write flaw was found in the way chrony stored certain addresses when configuring NTP or cmdmon access. An attacker that has the command key and is allowed to access cmdmon (only localhost is allowed by default) could use this flaw to crash chronyd or, possibly, execute arbitrary code with the privileges of the chronyd process.
(CVE-2015-1821)

An uninitialized pointer use flaw was found when allocating memory to save unacknowledged replies to authenticated command requests. An attacker that has the command key and is allowed to access cmdmon (only localhost is allowed by default) could use this flaw to crash chronyd or, possibly, execute arbitrary code with the privileges of the chronyd process. (CVE-2015-1822)

A denial of service flaw was found in the way chrony hosts that were peering with each other authenticated themselves before updating their internal state variables. An attacker could send packets to one peer host, which could cascade to other peers, and stop the synchronization process among the reached peers. (CVE-2015-1853)

The chrony packages have been upgraded to upstream version 2.1.1, which provides a number of bug fixes and enhancements over the previous version. Notable enhancements include :

  - Updated to NTP version 4 (RFC 5905)

  - Added pool directive to specify pool of NTP servers

  - Added leapsecmode directive to select how to correct     clock for leap second

  - Added smoothtime directive to smooth served time and     enable leap smear

  - Added asynchronous name resolving with POSIX threads

  - Ready for year 2036 (next NTP era)

  - Improved clock control

  - Networking code reworked to open separate client sockets     for each NTP server

This update also fixes the following bug :

  - The chronyd service previously assumed that network     interfaces specified with the 'bindaddress' directive     were ready when the service was started. This could     cause chronyd to fail to bind an NTP server socket to     the interface if the interface was not ready. With this     update, chronyd uses the IP_FREEBIND socket option,     enabling it to bind to an interface later, not only when     the service starts.

In addition, this update adds the following enhancement :

  - The chronyd service now supports four modes of handling     leap seconds, configured using the 'leapsecmode' option.
    The clock can be either stepped by the kernel (the     default 'system' mode), stepped by chronyd ('step'     mode), slowly adjusted by slewing ('slew' mode), or the     leap second can be ignored and corrected later in normal     operation ('ignore' mode). If you select slewing, the     correction will always start at 00:00:00 UTC and will be     applied at a rate specified in the 'maxslewrate' option.

The remote NewStart CGSL host, running version MAIN 6.02, has chrony packages installed that are affected by multiple vulnerabilities:

  - Multiple integer overflows in pktlength.c in Chrony before 1.29 allow remote attackers to cause a denial     of service (crash) via a crafted (1) REQ_SUBNETS_ACCESSED or (2) REQ_CLIENT_ACCESSES command request to     the PKL_CommandLength function or crafted (3) RPY_SUBNETS_ACCESSED, (4) RPY_CLIENT_ACCESSES, (5)     RPY_CLIENT_ACCESSES_BY_INDEX, or (6) RPY_MANUAL_LIST command reply to the PKL_ReplyLength function, which     triggers an out-of-bounds read or buffer overflow. NOTE: versions 1.27 and 1.28 do not require     authentication to exploit. (CVE-2012-4502)

  - cmdmon.c in Chrony before 1.29 allows remote attackers to obtain potentially sensitive information from     stack memory via vectors related to (1) an invalid subnet in a RPY_SUBNETS_ACCESSED command to the     handle_subnets_accessed function or (2) a RPY_CLIENT_ACCESSES command to the handle_client_accesses     function when client logging is disabled, which causes uninitialized data to be included in a reply.
    (CVE-2012-4503)

  - Chrony before 1.29.1 has traffic amplification in cmdmon protocol (CVE-2014-0021)

  - Heap-based buffer overflow in chrony before 1.31.1 allows remote authenticated users to cause a denial of     service (chronyd crash) or possibly execute arbitrary code by configuring the (1) NTP or (2) cmdmon access     with a subnet size that is indivisible by four and an address with a nonzero bit in the subnet remainder.
    (CVE-2015-1821)

  - chrony before 1.31.1 does not initialize the last next pointer when saving unacknowledged replies to     command requests, which allows remote authenticated users to cause a denial of service (uninitialized     pointer dereference and daemon crash) or possibly execute arbitrary code via a large number of command     requests. (CVE-2015-1822)

  - chrony before 1.31.1 does not properly protect state variables in authenticated symmetric NTP     associations, which allows remote attackers with knowledge of NTP peering to cause a denial of service     (inability to synchronize) via random timestamps in crafted NTP data packets. (CVE-2015-1853)

  - chrony before 1.31.2 and 2.x before 2.2.1 do not verify peer associations of symmetric keys when     authenticating packets, which might allow remote attackers to conduct impersonation attacks via an     arbitrary trusted key, aka a skeleton key. (CVE-2016-1567)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

As reported upstream :

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-2015-1821)

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. (CVE-2015-1822)

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. Authentication using a symmetric key can fully protect against this attack, but in implementations following the NTPv3 (RFC 1305) or NTPv4 (RFC 5905) specification the state variables were updated even when the authentication check failed and the association was not protected. (CVE-2015-1853)

ID	Name	Product	Family	Published	Updated	Severity
83067	Fedora 20 : chrony-1.31.1-1.fc20 (2015-5809)	Nessus	Fedora Local Security Checks	4/27/2015	1/11/2021	medium
86978	RHEL 7 : chrony (RHSA-2015:2241)	Nessus	Red Hat Local Security Checks	11/20/2015	12/18/2019	medium
82744	Debian DSA-3222-1 : chrony - security update	Nessus	Debian Local Security Checks	4/14/2015	1/11/2021	medium
87032	Oracle Linux 7 : chrony (ELSA-2015-2241)	Nessus	Oracle Linux Local Security Checks	11/24/2015	10/22/2024	medium
84531	GLSA-201507-01 : chrony: Multiple vulnerabilities	Nessus	Gentoo Local Security Checks	7/6/2015	1/11/2021	medium
82892	FreeBSD : chrony -- multiple vulnerabilities (c4571ca8-053d-44c9-ab3c-89b1372ad0a5)	Nessus	FreeBSD Local Security Checks	4/20/2015	1/6/2021	medium
82716	Debian DLA-193-1 : chrony security update	Nessus	Debian Local Security Checks	4/13/2015	1/11/2021	medium
87551	Scientific Linux Security Update : chrony on SL7.x x86_64 (20151119)	Nessus	Scientific Linux Local Security Checks	12/22/2015	1/14/2021	medium
154559	NewStart CGSL MAIN 6.02 : chrony Multiple Vulnerabilities (NS-SA-2021-0127)	Nessus	NewStart CGSL Local Security Checks	10/27/2021	11/27/2023	high
87146	CentOS 7 : chrony (CESA-2015:2241)	Nessus	CentOS Local Security Checks	12/2/2015	1/4/2021	medium
83009	Fedora 21 : chrony-1.31.1-1.fc21 (2015-5816)	Nessus	Fedora Local Security Checks	4/23/2015	1/11/2021	medium
83007	Fedora 22 : chrony-2.0-0.3.pre2.fc22 (2015-5748)	Nessus	Fedora Local Security Checks	4/23/2015	1/11/2021	medium
83978	Amazon Linux AMI : chrony (ALAS-2015-539)	Nessus	Amazon Linux Local Security Checks	6/4/2015	12/18/2019	medium

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