SOL17518 - NTP vulnerability CVE-2015-7871

Vulnerability Recommended Actions

If you are running a version listed in the Versions known to be vulnerable column, you can eliminate this vulnerability by upgrading to a version listed in theVersions known to be not vulnerable column. If the table lists only an older version than what you are currently running, or does not list a non-vulnerable version, then no upgrade candidate currently exists.

F5 responds to vulnerabilities in accordance with the Severityvalues published in the previous table. The Severity values and other security vulnerability parameters are defined in SOL4602: Overview of the F5 security vulnerability response policy.

Stepping time too far in either the future or past on F5 systems could cause services, such as Remote Authentication (Active Directory, Kerberos) and SSL/TLS certificate validation, which are time sensitive, to have unexpected results. Stepping the time too far into the future has the potential to expire BIG-IP licenses and cause unexpected behavior in the Configuration utility.

To mitigate this vulnerability, consider the following:

• Configure packet filters and/or Port Lockdown settings to restrict ingress NTP packets to Self IP addresses which come from untrusted sources.
• Configure the BIG-IP AFM system to restrict access to NTP services to both the management and/or self IP addresses.

For detection of successful exploitation, consider the following:

• Review the output of ntpq -p. If untrusted/unknown sources are listed, it is possible that an attacker has exploited this vulnerability.
• Monitor the**/var/log/ltm** file for the messageClock has unexpectedly adjusted by X ms. Note that this will show up in the** /var/log/ltm**file for 11.5.0 and later. These messages alone do not indicate there is a successful exploit, just that there are clock adjustments. If the frequency of these messages appears abnormal, examine the output of ntpq -p.
• Monitor the**/var/log/daemon.log**file for ntpd restarts and/or errors regarding time adjustments.

Supplemental Information

• SOL9970: Subscribing to email notifications regarding F5 products
• SOL9957: Creating a custom RSS feed to view new and updated documents
• SOL4918: Overview of the F5 critical issue hotfix policy