openvswitch: limitation in the OVS packet parsing in userspace leads to DoS (CVE-2020-35498)

Multiple versions of Open vSwitch are vulnerable to potential problems like denial of service attacks, in which crafted network packets could cause the packet lookup to ignore network header fields from layers 3 and 4.

Both kernel and userspace datapaths are affected, including DPDK enabled Open vSwitch (OVS-DPDK) as an example of the latter.

The crafted network packet is an ordinary IPv4 or IPv6 packet with Ethernet padding length above 255 bytes. This causes the packet sanity check to abort parsing header fields after layer 2.

When that situation happens, the classifier will use an unexpected set of header fields. This could cause the packet lookup to either match on unintended flows or return the default table miss action 'drop'.

As a consequence, the datapath can be instructed to match on an incorrect range of packets with an action to drop them, for example. Further legit traffic could hit the cached flow preventing it to expire extending the situation.

Fixed In Version:

openvswitch 2.14.2, 2.13.3, 2.12.3, 2.11.6, 2.10.7, 2.9.9, 2.8.11, 2.7.13, 2.6.10, 2.5.12

Reference:

https://www.openwall.com/lists/oss-security/2021/02/10/4

Patch:

https://github.com/openvswitch/ovs/commit/53c1b8b166f3dd217bc391d707885f789e9ecc49 (2.12)

Affected branches:

• master
• 3.13-stable