CVE-2023-28842 moby/moby's dockerd daemon encrypted overlay network with a single endpoint is unauthenticated
Attackers can bypass IPsec authentication on encrypted Docker Swarm overlay networks with a single endpoint, allowing unauthorized access to container traffic.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2023-28842?
CVE-2023-28842 is a medium-severity missing authorization vulnerability in moby, published on 4 Apr 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Moby) is an open source container framework developed by Docker Inc. that is distributed as Docker, Mirantis Container Runtime, and various other downstream projects/products. The Moby daemon component (`dockerd`), which is developed as moby/moby is commonly referred to as *Docker*.
Swarm Mode, which is compiled in and delivered by default in `dockerd` and is thus present in most major Moby downstreams, is a simple, built-in container orchestrator that is implemented through a combination of SwarmKit and supporting network code.
The `overlay` network driver is a core feature of Swarm Mode, providing isolated virtual LANs that allow communication between containers and services across the cluster. This driver is an implementation/user of VXLAN, which encapsulates link-layer (Ethernet) frames in UDP datagrams that tag the frame with the VXLAN metadata, including a VXLAN Network ID (VNI) that identifies the originating overlay network. In addition, the overlay network driver supports an optional, off-by-default encrypted mode, which is especially useful when VXLAN packets traverses an untrusted network between nodes.
Encrypted overlay networks function by encapsulating the VXLAN datagrams through the use of the IPsec Encapsulating Security Payload protocol in Transport mode. By deploying IPSec encapsulation, encrypted overlay networks gain the additional properties of source authentication through cryptographic proof, data integrity through check-summing, and confidentiality through encryption.
When setting an endpoint up on an encrypted overlay network, Moby installs three iptables (Linux kernel firewall) rules that enforce both incoming and outgoing IPSec. These rules rely on the `u32` iptables extension provided by the `xt_u32` kernel module to directly filter on a VXLAN packet's VNI field, so that IPSec guarantees can be enforced on encrypted overlay networks without interfering with other overlay networks or other users of VXLAN.
The `overlay` driver dynamically and lazily defines the kernel configuration for the VXLAN network on each node as containers are attached and detached. Routes and encryption parameters are only defined for destination nodes that participate in the network. The iptables rules that prevent encrypted overlay networks from accepting unencrypted packets are not created until a peer is available with which to communicate.
Encrypted overlay networks silently accept cleartext VXLAN datagrams that are tagged with the VNI of an encrypted overlay network. As a result, it is possible to inject arbitrary Ethernet frames into the encrypted overlay network by encapsulating them in VXLAN datagrams. The implications of this can be quite dire, and GHSA-vwm3-crmr-xfxw should be referenced for a deeper exploration.
Patches are available in Moby releases 23.0.3, and 20.10.24. As Mirantis Container Runtime's 20.10 releases are numbered differently, users of that platform should update to 20.10.16.
Some workarounds are available. In multi-node clusters, deploy a global ‘pause’ container for each encrypted overlay network, on every node. For a single-node cluster, do not use overlay networks of any sort. Bridge networks provide the same connectivity on a single node and have no multi-node features. The Swarm ingress feature is implemented using an overlay network, but can be disabled by publishing ports in `host` mode instead of `ingress` mode (allowing the use of an external load balancer), and removing the `ingress` network. If encrypted overlay networks are in exclusive use, block UDP port 4789 from traffic that has not been validated by IPSec.
Which versions are affected by CVE-2023-28842?
5 open source packages ship an affected version, including github.com/docker/docker. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/docker/docker Go | From 1.12.0 | 20.10.24+incompatible, 23.0.3+incompatible |
github.com/docker/docker Go | From 1.12.0 | 20.10.24 |
github.com/docker/docker Go | From 1.12.0 | 20.10.24 |
github.com/docker/docker Go | From 23.0.0 | 23.0.3 |
github.com/docker/docker Go | From 23.0.0 | 23.0.3 |
Products include Mobyproject Moby.
How do I fix CVE-2023-28842?
Upgrade github.com/docker/docker to a fixed version for your release line: 20.10.24+incompatible, 23.0.3+incompatible, 20.10.24 or 23.0.3.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2023-28842 being exploited?
There is no known exploitation of CVE-2023-28842 in the wild and no public exploit code.
Other vulnerabilities in moby
- CVE-2024-36623 Moby Race Condition vulnerability
- CVE-2023-28840 moby/moby's dockerd daemon encrypted overlay network may be unauthenticated
- CVE-2018-12608 Docker Authentication Bypass
- CVE-2024-24557 Moby classic builder cache poisoning
- CVE-2023-28841 moby/moby's dockerd daemon encrypted overlay network traffic may be unencrypted
Sources
Also known as CLEANSTART-2026-AL73661, CLEANSTART-2026-LH52703, DEBIAN-CVE-2023-28842, GHSA-6wrf-mxfj-pf5p, GO-2023-1701, UBUNTU-CVE-2023-28842.