CVE-2023-28841
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.
An iptables rule designates outgoing VXLAN datagrams with a VNI that corresponds to an encrypted overlay network for IPsec encapsulation.
Encrypted overlay networks on affected platforms silently transmit unencrypted data. As a result, overlay networks may appear to be functional, passing traffic as expected, but without any of the expected confidentiality or data integrity guarantees.
It is possible for an attacker sitting in a trusted position on the network to read all of the application traffic that is moving across the overlay network, resulting in unexpected secrets or user data disclosure. Thus, because many database protocols, internal APIs, etc. are not protected by a second layer of encryption, a user may use Swarm encrypted overlay networks to provide confidentiality, which due to this vulnerability this is no longer guaranteed.
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 outgoing traffic at the Internet boundary in order to prevent unintentionally leaking unencrypted traffic over the Internet, and/or ensure that the xt_u32 kernel module is available on all nodes of the Swarm cluster.
| Software | From | Fixed in |
|---|---|---|
github.com/docker/docker
|
1.12.0 | 20.10.24 |
|
github.com/docker/docker
|
23.0.0 | 23.0.3 |
| mobyproject / moby | 1.12.0 | 20.10.24 |
| mobyproject / moby | 23.0.0 | 23.0.3 |
- https://github.com/moby/libnetwork/blob/d9fae4c73daf76c3b0f77e14b45b8bf612ba764d/drivers/overlay/encryption.go#L205-L207
- https://github.com/moby/libnetwork/security/advisories/GHSA-gvm4-2qqg-m333
- https://github.com/moby/moby/issues/43382
- https://github.com/moby/moby/pull/45118
- https://github.com/moby/moby/security/advisories/GHSA-232p-vwff-86mp
- https://github.com/moby/moby/security/advisories/GHSA-33pg-m6jh-5237
- https://github.com/moby/moby/security/advisories/GHSA-6wrf-mxfj-pf5p
- https://github.com/moby/moby/security/advisories/GHSA-vwm3-crmr-xfxw
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/LYZOKMMVX4SIEHPJW3SJUQGMO5YZCPHC/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/XNF4OLYZRQE75EB5TW5N42FSXHBXGWFE/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/ZTE4ITXXPIWZEQ4HYQCB6N6GZIMWXDAI/
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A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
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Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
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