Security Advisory 0074 .CSAF
Date: April 1st, 2022
| Revision | Date | Changes |
|---|---|---|
| 1.0 | April 1st, 2022 | Initial Release |
The CVE-ID tracking this issue: CVE-2021-28504
CVSSv3.1 Base Score: 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N)
Common Weakness Enumeration: CWE-284 Improper Access Control
This vulnerability is being tracked by BUG 614735
Description
On affected platforms running Arista EOS, deny rules fail to get applied for packets of size higher than the configured maximum transmission unit (MTU), which results in packets of large size getting routed by the switch.
This issue was discovered internally and Arista is not aware of any malicious uses of this issue in customer networks.
Vulnerability Assessment
Affected Software
EOS Versions
- 4.27.1F and below releases in the 4.27.x train
- 4.26.3M and below releases in the 4.26.x train
- 4.25.6M and below releases in the 4.25.x train
Affected Platforms
The following products are affected by this vulnerability:
- CCS-750 series
- CCS-722XPM-48Y4-F
- CCS-722XPM-48ZY8-F
- DCS-7010TX-48 series
The following product versions and platforms are not affected by this vulnerability:
- Arista EOS-based products:
- 7010T series
- 7020R series
- 7050X/X2/X3/X4 series
- 7060X/X2/X3/X4/X5 series
- 7130 series
- 7150 series
- 7160 series
- 7170 series
- 720XP series
- 7250X series
- 7260X/X3 series
- 7280E/R/R2/R3 series
- 7300X/X3 series
- 7320X series
- 7358X4 series
- 7368X4 series
- 7388X5 series
- 7500E/R/R2/R3 series
- 7800R3 series
- Arista Wireless Access Points
- CloudVision WiFi virtual appliance or physical appliance
- CloudVision WiFi cloud service delivery
- CloudVision Portal, virtual appliance or physical appliance
- CloudVision as-a-Service
- Arista 7130 Systems running MOS
- Arista Converged Cloud Fabric and DANZ Monitoring Fabric (Formerly Big Switch Nodes for BCF and BMF)
- Awake Security Platform
Required Configuration for Exploitation
In order to be vulnerable to CVE-2021-28504 the following conditions must be all be met:
Routing should be enabled on the switch. To determine if routing is enabled on the switch,
switch# show running-config | include ip routing
ip routing
Layer3 interfaces must be active. To determine if L3 interfaces exist on the switch,
switch# show ip interface brief | exclude Management
Address
Interface IP Address Status Protocol MTU Owner
------------------- ---------------------- ------------ -------------------- ---------- -------
Vlan1000 unassigned up up 1500
Ingress data plane ACL should be applied to routed port / SVI. Run the following command to determine if “active on ingress” line has one or more L3 interfaces
switch# show ip access-lists deny summary IPV4 ACL deny Total rules configured: 1 Configured on Ingress: Et1/1,Vl1000 Active on Ingress: Et1/1,Vl1000 switch #show ip access-lists deny IP Access List deny 1 permit tcp any eq bgp any 2 permit tcp any any eq bgp 3 permit udp any any eq 179 4 permit udp any eq 179 any 10 deny ip any any
Indicators of Compromise
There are no indicators in logs and syslogs.
If configurations above are all met then, there is a potential for packets with length greater than configured / default MTU to be fragmented and routed via control-plane.
To check CPU forwarding run `show cpu counters queue | nz`. If `L3 Slow Path` queue shows an unexpected increase in the rate of packets forwarded by the CPU then this may be an indication of the issue.
switch# show cpu counters queue | nz ----------------------------------------------------------------------------------------------- SwitchcardCes1/0 ----------------------------------------------------------------------------------------------- Queue Counters/pkts Drops/pkts -----------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------- SwitchcardCes2/0 ----------------------------------------------------------------------------------------------- Queue Counters/pkts Drops/pkts ----------------------------------------------------------------------------------------------- L3 Slow Path 100 0
Mitigation
There is no mitigation / workaround for this issue.
Resolution
The recommended resolution is to upgrade to a remediated software version at your earliest convenience. Arista recommends customers move to the latest version of each release that contains all the fixes listed below.
CVE-2021-28504 has been fixed in the following releases:
- 4.27.2F and later releases in the 4.27.x train
- 4.26.4M and later releases in the 4.26.x train
- 4.25.7M and later releases in the 4.25.x train
For More Information
If you require further assistance, or if you have any further questions regarding this security notice, please contact the Arista Networks Technical Assistance Center (TAC) by one of the following methods:
Open a Service Request:
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By telephone: 408-547-5502 ; 866-476-0000