Package Instance

Moby's external DNS requests from 'internal' networks could lead to data exfiltration
Moby is an open source container framework originally developed by Docker Inc. as Docker. It is a key component of Docker Engine, Docker Desktop, and other distributions of container tooling or runtimes. As a batteries-included container runtime, Moby comes with a built-in networking implementation that enables communication between containers, and between containers and external resources.

Moby's networking implementation allows for creating and using many networks, each with their own subnet and gateway. This feature is frequently referred to as custom networks, as each network can have a different driver, set of parameters, and thus behaviors. When creating a network, the `--internal` flag is used to designate a network as _internal_. The `internal` attribute in a docker-compose.yml file may also be used to mark a network _internal_, and other API clients may specify the `internal` parameter as well.

When containers with networking are created, they are assigned unique network interfaces and IP addresses (typically from a non-routable [RFC 1918](https://datatracker.ietf.org/doc/html/rfc1918) subnet). The root network namespace (hereafter referred to as the 'host') serves as a router for non-internal networks, with a gateway IP that provides SNAT/DNAT to/from container IPs.

Containers on an _internal_ network may communicate between each other, but are precluded from communicating with any networks the host has access to (LAN or WAN) as no default route is configured, and firewall rules are set up to drop all outgoing traffic. Communication with the gateway IP address (and thus appropriately configured host services) is possible, and the host may communicate with any container IP directly.

In addition to configuring the Linux kernel's various networking features to enable container networking, `dockerd` directly provides some services to container networks. Principal among these is serving as a resolver, enabling service discovery (looking up other containers on the network by name), and resolution of names from an upstream resolver.

When a DNS request for a name that does not correspond to a container is received, the request is forwarded to the configured upstream resolver (by default, the host's configured resolver). This request is made from the container network namespace: the level of access and routing of traffic is the same as if the request was made by the container itself.

As a consequence of this design, containers solely attached to _internal_ network(s) will be unable to resolve names using the upstream resolver, as the container itself is unable to communicate with that nameserver. Only the names of containers also attached to the internal network are able to be resolved.

Many systems will run a local forwarding DNS resolver, typically present on a loopback address (`127.0.0.0/8`), such as systemd-resolved or dnsmasq. Common loopback address examples include `127.0.0.1` or `127.0.0.53`. As the host and any containers have separate loopback devices, a consequence of the design described above is that containers are unable to resolve names from the host's configured resolver, as they cannot reach these addresses on the host loopback device.

To bridge this gap, and to allow containers to properly resolve names even when a local forwarding resolver is used on a loopback address, `dockerd` will detect this scenario and instead forward DNS requests from the host/root network namespace. The loopback resolver will then forward the requests to its configured upstream resolvers, as expected.

## Impact

Because `dockerd` will forward DNS requests to the host loopback device, bypassing the container network namespace's normal routing semantics entirely, _internal_ networks can unexpectedly forward DNS requests to an external nameserver.

By registering a domain for which they control the authoritative nameservers, an attacker could arrange for a compromised container to exfiltrate data by encoding it in DNS queries that will eventually be answered by their nameservers. For example, if the domain `evil.example` was registered, the authoritative nameserver(s) for that domain could (eventually and indirectly) receive a request for `this-is-a-secret.evil.example`.

Docker Desktop is not affected, as Docker Desktop always runs an internal resolver on a RFC 1918 address.

## Patches

Moby releases 26.0.0-rc3, 25.0.5 (released) and 23.0.11 (to be released) are patched to prevent forwarding DNS requests from internal networks.

## Workarounds

-   Run containers intended to be solely attached to _internal_ networks with a custom upstream address (`--dns` argument to `docker run`, or API equivalent), which will force all upstream DNS queries to be resolved from the container network namespace.

## Background

- yair zak originally reported this issue to the Docker security team.
-  PR <https://github.com/moby/moby/pull/46609> was opened in public to fix this issue, as it was not originally considered to have a security implication.
- [The official documentation](https://docs.docker.com/network/drivers/ipvlan/#:~:text=If%20the%20parent,the%20network%20completely) claims that "the `--internal` flag that will completely isolate containers on a network from any communications external to that network," which necessitated this advisory and CVE.

Authz zero length regression
A security vulnerability has been detected in certain versions of Docker Engine, which could allow an attacker to bypass [authorization plugins (AuthZ)](https://docs.docker.com/engine/extend/plugins_authorization/) under specific circumstances. The base likelihood of this being exploited is low. This advisory outlines the issue, identifies the affected versions, and provides remediation steps for impacted users.

### Impact

Using a specially-crafted API request, an Engine API client could make the daemon forward the request or response to an [authorization plugin](https://docs.docker.com/engine/extend/plugins_authorization/) without the body. In certain circumstances, the authorization plugin may allow a request which it would have otherwise denied if the body had been forwarded to it.


A security issue was discovered In 2018,  where an attacker could bypass AuthZ plugins using a specially crafted API request. This could lead to unauthorized actions, including privilege escalation. Although this issue was fixed in Docker Engine [v18.09.1](https://docs.docker.com/engine/release-notes/18.09/#security-fixes-1) in January 2019, the fix was not carried forward to later major versions, resulting in a regression. Anyone who depends on authorization plugins that introspect the request and/or response body to make access control decisions is potentially impacted.

Docker EE v19.03.x and all versions of Mirantis Container Runtime **are not vulnerable.**

### Vulnerability details

- **AuthZ bypass and privilege escalation:** An attacker could exploit a bypass using an API request with Content-Length set to 0, causing the Docker daemon to forward the request without the body to the AuthZ plugin, which might approve the request incorrectly.
- **Initial fix:** The issue was fixed in Docker Engine [v18.09.1](https://docs.docker.com/engine/release-notes/18.09/#security-fixes-1) January 2019..
- **Regression:** The fix was not included in Docker Engine v19.03 or newer versions. This was identified in April 2024 and patches were released for the affected versions on July 23, 2024. The issue was assigned [CVE-2024-41110](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-41110).

### Patches

- docker-ce v27.1.1 containes patches to fix the vulnerability.
- Patches have also been merged into the master, 19.0, 20.0, 23.0, 24.0, 25.0, 26.0, and 26.1 release branches.

### Remediation steps

- If you are running an affected version, update to the most recent patched version.
- Mitigation if unable to update immediately:
    - Avoid using AuthZ plugins.
    - Restrict access to the Docker API to trusted parties, following the principle of least privilege.


### References

- https://github.com/moby/moby/commit/fc274cd2ff4cf3b48c91697fb327dd1fb95588fb
- https://github.com/moby/moby/commit/a79fabbfe84117696a19671f4aa88b82d0f64fc1
- https://www.docker.com/blog/docker-security-advisory-docker-engine-authz-plugin/

Moby Race Condition vulnerability
moby v25.0.5 is affected by a Race Condition in builder/builder-next/adapters/snapshot/layer.go. The vulnerability could be used to trigger concurrent builds that call the EnsureLayer function resulting in resource leaks/exhaustion.

Moby Race Condition vulnerability
moby v25.0.3 has a Race Condition vulnerability in the streamformatter package which can be used to trigger multiple concurrent write operations resulting in data corruption or application crashes.

Docker supplementary group permissions not set up properly, allowing attackers to bypass primary group restrictions
Moby is an open-source project created by Docker to enable software containerization. A bug was found in Moby (Docker Engine) where supplementary groups are not set up properly. If an attacker has direct access to a container and manipulates their supplementary group access, they may be able to use supplementary group access to bypass primary group restrictions in some cases, potentially gaining access to sensitive information or gaining the ability to execute code in that container.  This bug is fixed in Moby (Docker Engine) 20.10.18. Users should update to this version when it is available. Running containers should be stopped and restarted for the permissions to be fixed. For users unable to upgrade, this problem can be worked around by not using the `"USER $USERNAME"` Dockerfile instruction. Instead by calling `ENTRYPOINT ["su", "-", "user"]` the supplementary groups will be set up properly.

Thanks to Steven Murdoch for reporting this issue.

----

### Impact

If an attacker has direct access to a container and manipulates their supplementary group access, they may be able to use supplementary group access to bypass primary group restrictions in some cases, potentially gaining access to sensitive information or gaining the ability to execute code in that container. 

### Patches

 This bug is fixed in Moby (Docker Engine) 20.10.18. Users should update to this version when it is available.

### Workarounds

This problem can be worked around by not using the `"USER $USERNAME"` Dockerfile instruction. Instead by calling `ENTRYPOINT ["su", "-", "user"]` the supplementary groups will be set up properly.

### References

https://www.benthamsgaze.org/2022/08/22/vulnerability-in-linux-containers-investigation-and-mitigation/

### For more information

If you have any questions or comments about this advisory:

* [Open an issue](https://github.com/moby/moby/issues/new)
* Email us at [security@docker.com](mailto:security@docker.com)

IPv6 enabled on IPv4-only network interfaces
In 26.0.0 and 26.0.1, IPv6 is not disabled on network interfaces, including those belonging to networks where `--ipv6=false`.

### Impact

A container with an `ipvlan` or `macvlan` interface will normally be configured to share an external network link with the host machine. Because of this direct access, with IPv6 enabled:

- Containers may be able to communicate with other hosts on the local network over link-local IPv6 addresses.
- If router advertisements are being broadcast over the local network, containers may get SLAAC-assigned addresses.
- The interface  will be a member of IPv6 multicast groups.

This means interfaces in IPv4-only networks present an unexpectedly and unnecessarily increased attack surface.

A container with an unexpected IPv6 address can do anything a container configured with an IPv6 address can do. That is, listen for connections on its IPv6 address, open connections to other nodes on the network over IPv6, or attempt a DoS attack by flooding packets from its IPv6 address. This has CVSS score AV:L/AC:H/PR:N/UI:R/S:C/C:N/I:N/A:L (2.7).

Because the container may not be constrained by an IPv6 firewall, there is increased potential for data exfiltration from the container. This has CVSS score AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N (4.7).

A remote attacker could send malicious Router Advertisements to divert traffic to itself, a black-hole, or another device. The same attack is possible today for IPv4 macvlan/ipvlan endpoints with ARP spoofing, TLS is commonly used by Internet APIs to mitigate this risk. The presence of an IPv6 route could impact the container's availability by indirectly abusing the behaviour of software which behaves poorly in a dual-stack environment. For example, it could resolve a name to a DNS AAAA record and keep trying to connect over IPv6 without ever falling back to IPv4, potentially denying service to the container. This has CVSS score AV:A/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H (4.5).

### Patches

The issue is patched in 26.0.2.

### Workarounds

To completely disable IPv6 in a container, use `--sysctl=net.ipv6.conf.all.disable_ipv6=1` in the `docker create` or `docker run` command. Or, in the service configuration of a `compose` file, the equivalent:

```
        sysctls:
            - net.ipv6.conf.all.disable_ipv6=1
```

### References

- sysctl configuration using `docker run`:
  - https://docs.docker.com/reference/cli/docker/container/run/#sysctl
- sysctl configuration using `docker compose`:
  - https://docs.docker.com/compose/compose-file/compose-file-v3/#sysctls

Docker Swarm encrypted overlay network may be unauthenticated
[Moby](https://mobyproject.org/) 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](https://github.com/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](https://github.com/moby/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](https://en.wikipedia.org/wiki/Virtual_Extensible_LAN), 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](https://en.wikipedia.org/wiki/IPsec#Encapsulating_Security_Payload) protocol in [Transport mode](https://en.wikipedia.org/wiki/IPsec#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](https://www.netfilter.org/projects/iptables/index.html) (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](https://github.com/moby/libnetwork/blob/d9fae4c73daf76c3b0f77e14b45b8bf612ba764d/drivers/overlay/encryption.go#L230-L234) 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.

On Red Hat Enterprise Linux and derivatives such as CentOS and Rocky, the `xt_u32` module has been:
* [moved to the kernel-modules-extra package and no longer installed by default in RHEL 8.3](https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/8.3_release_notes/rhel-8-3-0-release#technology-preview_networking)
* [officially deprecated in RHEL 8.6](https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/8.6_release_notes/deprecated_functionality#deprecated-functionality_networking)
* [removed completely in RHEL 9](https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/9/html/considerations_in_adopting_rhel_9/assembly_networking_considerations-in-adopting-rhel-9#ref_firewall-networking_assembly_networking)

These rules are not created when `xt_u32` is unavailable, even though the container is still attached to the network.

## Impact
Encrypted overlay networks on affected configurations 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 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
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.

## Workarounds
* Close the VXLAN port (by default, UDP port 4789) to incoming traffic at the Internet boundary (see [GHSA-vwm3-crmr-xfxw](https://github.com/moby/moby/security/advisories/GHSA-vwm3-crmr-xfxw)) to prevent all VXLAN packet injection.
* Ensure that the `xt_u32` kernel module is available on all nodes of the Swarm cluster.

## Background
* [#43382](https://github.com/moby/moby/issues/43382) partially discussed this concern, but did not consider the security implications.
* Mirantis FIELD-5788 essentially duplicates [#43382](https://github.com/moby/moby/issues/43382), and was created six months earlier; it similarly overlooked the security implications.
* [#45118](https://github.com/moby/moby/pull/45118) is the ancestor of the final patches, and was where the security implications were discovered.

## Related
* [CVE-2023-28841: Encrypted overlay network traffic may be unencrypted](https://github.com/moby/moby/security/advisories/GHSA-33pg-m6jh-5237)
* [CVE-2023-28842: Encrypted overlay network with a single endpoint is unauthenticated](https://github.com/moby/moby/security/advisories/GHSA-6wrf-mxfj-pf5p)
* [GHSA-vwm3-crmr-xfxw: The Swarm VXLAN port may be exposed to attack due to ambiguous documentation](https://github.com/moby/moby/security/advisories/GHSA-vwm3-crmr-xfxw)
* [GHSA-gvm4-2qqg-m333: Security issues in encrypted overlay networks](https://github.com/moby/libnetwork/security/advisories/GHSA-gvm4-2qqg-m333) (libnetwork)

Docker Swarm encrypted overlay network with a single endpoint is unauthenticated
[Moby](https://mobyproject.org/) 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](https://github.com/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](https://github.com/moby/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](https://en.wikipedia.org/wiki/Virtual_Extensible_LAN), 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](https://en.wikipedia.org/wiki/IPsec#Encapsulating_Security_Payload) protocol in [Transport mode](https://en.wikipedia.org/wiki/IPsec#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](https://www.netfilter.org/projects/iptables/index.html) (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.

## Impact
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](https://github.com/moby/moby/security/advisories/GHSA-vwm3-crmr-xfxw) should be referenced for a deeper exploration.

## Patches
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.

## Workarounds
* In multi-node clusters, deploy a global ‘pause’ container for each encrypted overlay network, on every node. For example, use the `registry.k8s.io/pause` image and a `--mode global` service.
* 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. For example, `iptables -A INPUT -m udp —-dport 4789 -m policy --dir in --pol none -j DROP`.

## Background
* This issue was discovered while characterizing and mitigating [CVE-2023-28840](https://github.com/moby/moby/security/advisories/GHSA-232p-vwff-86mp) and [CVE-2023-28841](https://github.com/moby/moby/security/advisories/GHSA-33pg-m6jh-5237).

## Related
* [CVE-2023-28841: Encrypted overlay network traffic may be unencrypted](https://github.com/moby/moby/security/advisories/GHSA-33pg-m6jh-5237)
* [CVE-2023-28840: Encrypted overlay network may be unauthenticated](https://github.com/moby/moby/security/advisories/GHSA-232p-vwff-86mp)
* [GHSA-vwm3-crmr-xfxw: The Swarm VXLAN port may be exposed to attack due to ambiguous documentation](https://github.com/moby/moby/security/advisories/GHSA-vwm3-crmr-xfxw)
* [GHSA-gvm4-2qqg-m333: Security issues in encrypted overlay networks](https://github.com/moby/libnetwork/security/advisories/GHSA-gvm4-2qqg-m333) (libnetwork)