CVE-2023-28840 moby/moby's dockerd daemon encrypted overlay network may be unauthenticated
Attackers can bypass IPsec authentication on encrypted Docker Swarm overlay networks, potentially intercepting or injecting traffic between nodes.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2023-28840?
CVE-2023-28840 is a high-severity authentication bypass 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 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.
Two iptables rules serve to filter incoming VXLAN datagrams with a VNI that corresponds to an encrypted network and discards unencrypted datagrams. The rules are appended to the end of the INPUT filter chain, following any rules that have been previously set by the system administrator. Administrator-set rules take precedence over the rules Moby sets to discard unencrypted VXLAN datagrams, which can potentially admit unencrypted datagrams that should have been discarded.
The injection of arbitrary Ethernet frames can enable a Denial of Service attack. A sophisticated attacker may be able to establish a UDP or TCP connection by way of the container’s outbound gateway that would otherwise be blocked by a stateful firewall, or carry out other escalations beyond simple injection by smuggling packets into the overlay network.
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. Close the VXLAN port (by default, UDP port 4789) to incoming traffic at the Internet boundary to prevent all VXLAN packet injection, and/or ensure that the `xt_u32` kernel module is available on all nodes of the Swarm cluster.
Which versions are affected by CVE-2023-28840?
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 |
Linux distribution packages (1)
docker-compose openSUSE:Tumbleweed | All versions | 2.17.3-1.1 |
Products include Mobyproject Moby.
How do I fix CVE-2023-28840?
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 rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2023-28840 being exploited?
There is no known exploitation of CVE-2023-28840 in the wild and no public exploit code.
Other vulnerabilities in moby
- CVE-2024-36623 Moby Race Condition vulnerability
- 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
- CVE-2023-28842 moby/moby's dockerd daemon encrypted overlay network with a single endpoint is unauthenticated
Sources
Also known as CLEANSTART-2026-IW20261, CLEANSTART-2026-JQ26035, DEBIAN-CVE-2023-28840, GHSA-232p-vwff-86mp, GO-2023-1699, UBUNTU-CVE-2023-28840 and 1 more.