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 packets 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 Runtimes 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.

Weakness

The product does not encrypt sensitive or critical information before storage or transmission.

Affected Software

Potential Mitigations

• Ensure that encryption is properly integrated into the system design, including but not necessarily limited to:

• Identify the separate needs and contexts for encryption:

• Using threat modeling or other techniques, assume that data can be compromised through a separate vulnerability or weakness, and determine where encryption will be most effective. Ensure that data that should be private is not being inadvertently exposed using weaknesses such as insecure permissions (CWE-732). [REF-7]

• When there is a need to store or transmit sensitive data, use strong, up-to-date cryptographic algorithms to encrypt that data. Select a well-vetted algorithm that is currently considered to be strong by experts in the field, and use well-tested implementations. As with all cryptographic mechanisms, the source code should be available for analysis.

• For example, US government systems require FIPS 140-2 certification.

• Do not develop custom or private cryptographic algorithms. They will likely be exposed to attacks that are well-understood by cryptographers. Reverse engineering techniques are mature. If the algorithm can be compromised if attackers find out how it works, then it is especially weak.

• Periodically ensure that the cryptography has not become obsolete. Some older algorithms, once thought to require a billion years of computing time, can now be broken in days or hours. This includes MD4, MD5, SHA1, DES, and other algorithms that were once regarded as strong. [REF-267]

• Compartmentalize the system to have “safe” areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area.

• Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/157.html
• https://cwe.mitre.org/data/definitions/158.html
• https://cwe.mitre.org/data/definitions/204.html
• https://cwe.mitre.org/data/definitions/31.html
• https://cwe.mitre.org/data/definitions/37.html
• https://cwe.mitre.org/data/definitions/383.html
• https://cwe.mitre.org/data/definitions/384.html
• https://cwe.mitre.org/data/definitions/385.html
• https://cwe.mitre.org/data/definitions/386.html
• https://cwe.mitre.org/data/definitions/387.html
• https://cwe.mitre.org/data/definitions/388.html
• https://cwe.mitre.org/data/definitions/477.html
• https://cwe.mitre.org/data/definitions/609.html
• https://cwe.mitre.org/data/definitions/65.html

References

• 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/