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Date: Thu, 6 Apr 2023 19:55:29 +0200
From: Ilya Maximets <i.maximets@....org>
To: oss-security@...ts.openwall.com, ovs-announce@...nvswitch.org,
ovs-discuss <ovs-discuss@...nvswitch.org>
Cc: i.maximets@....org, Aaron Conole <aconole@...hat.com>,
Flavio Leitner <fbl@...hat.com>, David Marchand <david.marchand@...hat.com>
Subject: Re: [ADVISORY] CVE-2023-1668: Open vSwitch: Remote traffic denial of
service via crafted packets with IP proto 0
On 4/6/23 19:37, Ilya Maximets wrote:
> Description
> ===========
>
> Multiple versions of Open vSwitch are vulnerable to crafted IP packets
> with ip proto set to 0 causing a potential denial of service.
> Triggering the vulnerability will require an attacker to send a crafted
> IP packet with protocol field set to 0 and the flow rules to contain
> 'set' actions on other fields in the IP protocol header. The resulting
> flows will omit required actions, and fail to mask the IP protocol field,
> resulting in a large bucket which captures all IP packets.
>
> All versions of Open vSwitch at least as early as 1.5.0 are affected.
>
> The Common Vulnerabilities and Exposures project (cve.mitre.org) has
> assigned the identifier CVE-2023-1668 to this issue.
>
>
> Mitigation
> ==========
>
> For any version of Open vSwitch, preventing packets with network
> protocol number '0' from reaching Open vSwitch will prevent the issue.
> This is difficult to achieve because Open vSwitch obtains packets before
> the iptables or nftables host firewall, so iptables or nftables on the
> Open vSwitch host cannot ordinarily block the vulnerability.
>
> Another method would be to add a high priority rule to the flow table
> explicitly matching on nw protocol '0' and handling that traffic
> separately:
>
> table=0 priority=32768,ip,nw_proto=0,actions=drop
> table=0 priority=32768,ipv6,nw_proto=0,actions=drop
> table=0 priority=32768,arp,arp_op=0,actions=drop
Correction:
Priorities for these flows should be set to 65535 instead.
i.e. The maximum priority that can be set with OpenFlow.
>
> All 3 OpenFlow rules should be added to every OVS bridge. This can
> be difficult to maintain during the service restart.
>
>
> Fix
> ===
>
> Patches to fix these vulnerabilities in Open vSwitch 2.13.x and newer:
>
> * 3.1.x:
> https://github.com/openvswitch/ovs/commit/61b39d8c4797f1b668e4d5e5350d639fca6082a9
> * 3.0.x:
> https://github.com/openvswitch/ovs/commit/0ec9af260ad84225e758d249fa32151ddf8a6520
> * 2.17.x:
> https://github.com/openvswitch/ovs/commit/27fb5db7f727ffc056f024f9ba4936facccb5f40
> * 2.16.x:
> https://github.com/openvswitch/ovs/commit/42f2b4b9b9a3c11d38f180bf1e35c47b77cd4ce8
> * 2.15.x:
> https://github.com/openvswitch/ovs/commit/f36509fd64e339ffd33593451099be6baa12ffe6
> * 2.14.x:
> https://github.com/openvswitch/ovs/commit/b46505f4d26cd4612a533687e7884efcb7a74111
> * 2.13.x:
> https://github.com/openvswitch/ovs/commit/7fa0106e8594c34f9e16efd87a58e38a947c6c5b
>
>
> Recommendation
> ==============
>
> We recommend that users of Open vSwitch apply the linked patches, or
> upgrade to a known patched version of Open vSwitch. These include:
>
> * 3.1.1
> * 3.0.4
> * 2.17.6
> * 2.16.7
> * 2.15.8
> * 2.14.9
> * 2.13.11
>
>
> Acknowledgements
> ================
>
> The Open vSwitch team wishes to thank the reporter:
>
> David Marchand <dmarchan@...hat.com>
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