CVE-2017-3144: Failure to properly clean up closed OMAPI connections can exhaust available sockets

AA-01541

Document Version: 
2.0
Posting date: 
16 Jan 2018
Program Impacted: 
DHCP
Versions affected: 
4.1.0 to 4.1-ESV-R15, 4.2.0 to 4.2.8, 4.3.0 to 4.3.6.  Older versions may also be affected but are well beyond their end-of-life (EOL).  Releases prior to 4.1.0 have not been tested.
Severity:
Medium
Exploitable: 
Remotely (if attackers are permitted access to a server's OMAPI control port)

Description:

A vulnerability stemming from failure to properly clean up closed OMAPI connections can lead to exhaustion of the pool of socket descriptors available to the DHCP server.

Impact:

By intentionally exploiting this vulnerability an attacker who is permitted to establish connections to the OMAPI control port can exhaust the pool of socket descriptors available to the DHCP server.

Once exhausted, the server will not accept additional connections, potentially denying access to legitimate connections from the server operator.  While the server will continue to receive and service DHCP client requests, the operator can be blocked from the ability to use OMAPI to control server state, add new lease reservations, etc.

CVSS Score:  5.3

CVSS Vector:  CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

For more information on the Common Vulnerability Scoring System and to obtain your specific environmental score please visit: https://www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Workarounds:

The recommended remedy is to disallow access to the OMAPI control port from unauthorized clients (in accordance with best practices for server operation).

Active exploits:

None known.

Solution: 

ISC has written a patch which properly cleans up closed socket connections and will include it in future maintenance releases of ISC DHCP.  The patch is also available upon request (to security-officer@isc.org) to parties who want to incorporate it into their own code before the next ISC maintenance releases.  However, we do not plan to issue a special security patch release of DHCP to address this particular issue because we have concluded that the workaround of denying OMAPI connections from unauthorized client addresses should be sufficient in almost all cases and is a recommended best practice for server operation.

Document Revision History:

1.0 Advance notification, 08 January 2018
2.0 Public disclosure, 16 January 2018

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Note:

ISC patches only currently supported versions. When possible we indicate EOL versions affected.  (For current information on which versions are actively supported, please see http://www.isc.org/downloads/). 

ISC Security Vulnerability Disclosure Policy:  Details of our current security advisory policy and practice can be found here: https://kb.isc.org/article/AA-00861

This Knowledge Base article https://kb.isc.org/article/AA-01541 is the complete and official security advisory document.

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