NTP BUG 3012(p12 update): Sybil vulnerability: ephemeral association attack
Last update: April 22, 2024 18:49 UTC (7e7bd5857)
Summary
| Resolved |
4.2.8p12 (Improve noepeer behavior.) |
14 Aug 2018 |
| References |
Bug 3012 |
CVE-2018-7170
While fixed in ntp-4.2.8p7 and with significant additional protections for this issue in 4.2.8p11, ntp-4.2.8p12 includes a fix for an edge case in the new noepeer support. Refer to CVE-2016-1549 for additional info. |
| Affects |
All ntp-4 releases up to, but not including 4.2.8p7, and 4.3.0 up to, but not including 4.3.94. |
Resolved in 4.2.8p11. Improved in 4.2.8p12 and 4.3.94. |
| CVSS2 Score |
LOW 3.5 |
AV:N/AC:M/Au:S/C:N/I:P/A:N |
| CVSS3 Score |
MED 5.3 |
CVSS:3.0/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N |
Description
ntpd can be vulnerable to Sybil attacks. If a system is set up to use a trustedkey and if one is not using the feature introduced in ntp-4.2.8p6 allowing an optional 4th field in the ntp.keys file to specify which IPs can serve time, a malicious authenticated peer – i.e. one where the attacker knows the private symmetric key – can create arbitrarily-many ephemeral associations in order to win the clock selection of ntpd and modify a victim’s clock. Two additional protections are offered in ntp-4.2.8p11. One is the noepeer directive, which disables symmetric passive ephemeral peering. The other extends the functionality of the 4th field in the ntp.keys file to include specifying a subnet range.
Mitigation
- Implement BCP-38.
- Upgrade to 4.2.8p12 or later.
- Use the
noepeer directive to prohibit symmetric passive ephemeral associations.
- Use the
ippeerlimit directive to limit the number of peer associations from an IP.
- Use the 4th argument in the
ntp.keys file to limit the IPs and subnets that can be time servers.
- Properly monitor your
ntpd instances.
Credit
This weakness was originally discovered by Matthew Van Gundy of Cisco ASIG. The edge-case hole in the noepeer processing was reported by Martin Burnicki of Meinberg.
Timeline