2020-10 Security Bulletin: Junos OS: EX4600, QFX5K Series: Stateless firewall filter matching 'user-vlan-id' will cause incomplete discard action (CVE-2020-1685)

Product Affected:

This issue affects Junos OS 18.1, 18.2, 18.3, 18.4, 19.1, 19.2. Affected platforms: EX4600, QFX5K Series.

Problem:

When configuring stateless firewall filters in Juniper Networks EX4600 and QFX 5000 Series devices using Virtual Extensible LAN protocol (VXLAN), the discard action will fail to discard traffic under certain conditions. Given a firewall filter configuration similar to:

  family ethernet-switching {
    filter L2-VLAN {
        term ALLOW {
            from {
                user-vlan-id 100;
            }
            then {
                accept;
            }
        }
        term NON-MATCH {
            then {
                discard;
            }
        }

when there is only one term containing a 'user-vlan-id' match condition, and no other terms in the firewall filter except discard, the discard action for non-matching traffic will only discard traffic with the same VLAN ID specified under 'user-vlan-id'. Other traffic (e.g. VLAN ID 200) will not be discarded. This unexpected behavior can lead to unintended traffic passing through the interface where the firewall filter is applied.

This issue only affects systems using VXLANs.

This issue affects Juniper Networks Junos OS on QFX5K Series:

18.1 versions prior to 18.1R3-S7, except 18.1R3;
18.2 versions prior to 18.2R2-S7, 18.2R3-S1;
18.3 versions prior to 18.3R1-S5, 18.3R2-S4, 18.3R3;
18.4 versions prior to 18.4R1-S7, 18.4R2-S1, 18.4R3;
19.1 versions prior to 19.1R1-S5, 19.1R2;
19.2 versions prior to 19.2R1-S5, 19.2R2.

A sample VXLAN configuration is shown below:

 evpn {
    encapsulation vxlan;
  }

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

This issue was found during internal product security testing or research.

This issue has been assigned CVE-2020-1685.

Solution:

The following software releases have been updated to resolve this specific issue: Junos OS 18.1R3-S7, 18.2R2-S7, 18.2R3-S1, 18.3R1-S5, 18.3R2-S4, 18.3R3, 18.4R1-S7, 18.4R2-S1, 18.4R3, 19.1R1-S5, 19.1R2, 19.2R1-S5, 19.2R2, 19.3R1, and all subsequent releases.

This issue is being tracked as 1446489.

Workaround:

Avoid using the user-vlan-id match criteria.

Implementation:

Software releases or updates are available for download at https://www.juniper.net/support/downloads/.

Modification History:

2020-10-14: Initial Publication

CVSS Score:

5.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N)

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."

Knowledge Base