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2021-07 Security Bulletin: Junos OS Evolved: Authenticated denial of service in ntpd (CVE-2019-8936)



Article ID: JSA11179 SECURITY_ADVISORIES Last Updated: 14 Jul 2021Version: 2.0
Product Affected:
This issue affects Junos OS Evolved All versions prior to 20.4, 21.1, 21.2.

On Juniper Networks Junos OS Evolved devices where ntp is enabled a crafted malicious authenticated mode 6 packet from a permitted network address can trigger a NULL pointer dereference. Note for this attack to work, the sending system must be on an address from which the target ntpd accepts mode 6 packets, and must use a private key that is specifically listed as being used for mode 6 authorization. The ntpd daemon can crash due to the NULL pointer dereference, causing a Denial of Service (DoS).

Continued receipt and processing of these crafted malicious packets will create a sustained Denial of Service (DoS) condition.

This issue affects:

Juniper Networks Junos OS Evolved

  • All versions prior to 20.4R2-S2-EVO;
  • 21.1 versions prior to 21.1R2-EVO;
  • 21.2 versions prior to 21.2R1-EVO.

The following minimal configuration example is provided:

[system ntp]

Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

This issue was discovered during external security research.

This issue has been assigned CVE-2019-8936.


The following software releases have been updated to resolve this specific issue: Junos OS Evolved: 20.4R2-S2-EVO, 21.1R2-EVO, 21.2R1-EVO, and all subsequent releases.

This issue is being tracked as 1589449.

Use 'restrict noquery' options in the ntpd configuration to limit addresses that can send mode 6 queries.
Software releases or updates are available for download at
Modification History:
2021-07-14: Initial Publication.

CVSS Score:
7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
Severity Level:
Severity Assessment:
Information for how Juniper Networks uses CVSS can be found at KB 16446 "Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories."

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