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2021-04 Security Bulletin: Junos OS: MX Series: Executing CLI command repetitively may cause the system to run out of disk space (CVE-2021-0238)

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Article ID: JSA11133 SECURITY_ADVISORIES Last Updated: 14 Apr 2021Version: 1.0
Product Affected:
This issue affects Junos OS 17.3, 17.4, 18.1, 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1, 20.2, 20.3, 20.4. Affected platforms: MX Series.
Problem:

When a MX Series is configured as a Broadband Network Gateway (BNG) based on Layer 2 Tunneling Protocol (L2TP), executing certain CLI command may cause the system to run out of disk space, excessive disk usage may cause other complications.

An administrator can use the following CLI command to monitor the available disk space:

user@device> show system storage
Filesystem Size Used Avail Capacity Mounted on
/dev/gpt/junos 19G 18G 147M 99% /.mount <<<<< running out of space
tmpfs 21G 16K 21G 0% /.mount/tmp
tmpfs 5.3G 1.7M 5.3G 0% /.mount/mfs

This issue affects Juniper Networks Junos OS on MX Series:

  • 17.3R1 and later versions prior to 17.4R3-S5,
  • 18.1 versions prior to 18.1R3-S13,
  • 18.2 versions prior to 18.2R3-S7;
  • 18.3 versions prior to 18.3R3-S4;
  • 18.4 versions prior to 18.4R3-S7;
  • 19.1 versions prior to 19.1R3-S4;
  • 19.2 versions prior to 19.2R1-S6, 19.2R3-S2;
  • 19.3 versions prior to 19.3R3-S2;
  • 19.4 versions prior to 19.4R2-S4, 19.4R3-S2;
  • 20.1 versions prior to 20.1R3;
  • 20.2 versions prior to 20.2R2-S3, 20.2R3;
  • 20.3 versions prior to 20.3R2;
  • 20.4 versions prior to 20.4R1-S1, 20.4R2;

This issue does not affect Juniper Networks Junos OS versions prior to 17.3R1.

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

This issue was seen during production usage.

This issue has been assigned CVE-2021-0238.

Solution:

The following software releases have been updated to resolve this specific issue: 17.4R3-S5, 18.1R3-S13, 18.2R3-S7, 18.3R3-S4, 18.4R3-S7, 19.1R3-S4, 19.2R1-S6, 19.2R3-S2, 19.3R3-S2, 19.4R2-S4, 19.4R3-S2, 20.1R3, 20.2R2-S3, 20.2R3, 20.3R2, 20.4R1-S1, 20.4R2, 21.1R1, and all subsequent releases.

If impacted, issue is recoverable after restarting the jl2tpd daemon:

user@device> restart l2tp-universal-edge

This issue is being tracked as 1537772.

Workaround:

There are no viable workarounds for this issue.

To reduce the risk of exploitation of this issue, use access lists or firewall filters to limit access to the CLI only trusted administrative networks, hosts and users.

Implementation:
Software releases or updates are available for download at https://support.juniper.net/support/downloads/
Modification History:
2021-04-14: Initial Publication.
CVSS Score:
5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)
Severity Level:
Medium
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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