NTP Bug 3379

NTP-01-004 NTP: Potential Overflows in ctl_put() functions (Medium)

• Date Resolved: 21 Mar 2017
• References: Sec 3379 / CVE-2017-6458 / VU#325339
• Affects: All versions of NTP, up to but not including ntp-4.2.8p10, and ntp-4.3.0 up to, but not including ntp-4.3.94.
• CVSS2: MED 4.6 (AV:N/AC:H/Au:M/C:N/I:N/A:C)
• CVSS3: MED 4.2 CVSS:3.0/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:N/A:H
• Summary: ntpd makes use of different wrappers around ctl_putdata() to create name/value ntpq (mode 6) response strings. For example, ctl_putstr() is usually used to send string data (variable names or string data). The formatting code was missing a length check for variable names. If somebody explicitly created any unusually long variable names in ntpd (longer than 200-512 bytes, depending on the type of variable), then if any of these variables are added to the response list it would overflow a buffer.
• Mitigation:
  • Implement BCP-38.
  • Upgrade to 4.2.8p10, or later, from the NTP Project Download Page or the NTP Public Services Project Download Page
  • If you don't want to upgrade, then don't setvar variable names longer than 200-512 bytes in your ntp.conf file.
  • Properly monitor your ntpd instances, and auto-restart ntpd (without -g) if it stops running.
• Credit: This weakness was discovered by Cure53.