On affected platforms running Arista EOS with Open Shortest Path First version 3 (OSPFv3) configured, an unauthenticated attacker on the same OSPFv3 broadcast domain can send a specially crafted set of packets that can cause the Ospf3 agent to restart unexpectedly. The crash results in the loss of all OSPFv3 adjacencies on the affected device and may disrupt routing across the broader OSPF domain until the agent recovers.
This issue was reported externally by Dravanet Inc., and Arista is not aware of any malicious exploitation of this vulnerability in customer networks.
In order to be vulnerable to CVE-2026-73438, the following condition must be met:
OSPFv3 must be configured:
switch>show ospfv3
OSPFv3 address-family ipv4
Routing Process "ospfv3" with ID 10.1.1.5 and Instance 64 VRF default
...
OSPFv3 address-family ipv6
Routing Process "ospfv3" with ID 10.1.1.5 and Instance 0 VRF default
...
or
switch>show ipv6 ospf
Routing Process "ospfv3 0" with ID 10.1.1.5 and Instance 0 VRF default
...
If the commands produce no output, then OSPFv3 is not configured:
switch>show ospfv3
switch>show ipv6 ospf
The OSPFv3 authentication feature helps to mitigate this vulnerability. OSPFv3 authentication prevents unauthorized actors from injecting crafted packets into the OSPF domain. Enabling it on all OSPFv3-speaking interfaces ensures that packets from unauthenticated senders are discarded before they can trigger this vulnerability.
Per-interface OSPFv3 encryption:
Configure ESP-based encryption with authentication on each OSPFv3 interface. All peers on the same interface must use the same SPI, algorithm, and passphrase.
switch(config)# interface <interface-name>
switch(config-if)# ospfv3 encryption ipsec spi <spi-value> esp aes-256-cbc sha1 passphrase <shared-passphrase>
Per-area OSPFv3 configuration:
Configure ESP-based encryption with authentication on each OSPFv3 area.
switch(config)# router ospfv3
switch(config-router-ospfv3)# address-family ipv4
switch(config-router-ospfv3-af)# area <area-id> encryption ipsec spi <spi-value> esp aes-256-cbc sha1 passphrase <shared-passphrase>
switch(config-router-ospfv3-af)# address-family ipv6
switch(config-router-ospfv3-af)# area <area-id> encryption ipsec spi <spi-value> esp aes-256-cbc sha1 passphrase <shared-passphrase>
Caution: Enabling OSPFv3 authentication must be coordinated across peering neighbors simultaneously. Applying this configuration to a single peer will temporarily break the routing adjacency, resulting in traffic disruption.
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-2026-73438 has been fixed in the following releases:
- 4.36.2F and later releases in the 4.36.x train
- 4.35.6M and later releases in the 4.35.x train
- 4.34.8M and later releases in the 4.34.x train
- 4.33.10M and later releases in the 4.33.x train
No hotfix is available for this issue.