Apollo Router Coprocessors may cause Denial-of-Service when handling request bodies

Impact

Instances of the Apollo Router using either of the following may be impacted by a denial-of-service vulnerability.

1. External Coprocessing with specific configurations; or
2. Native Rust Plugins accessing the Router request body in the RouterService layer

Router customizations using Rhai scripts are not impacted.

When using External Coprocessing:

Instances of the Apollo Router running versions >=1.21.0 and <1.52.1 are impacted by a denial-of-service vulnerability if all of the following are true:

1. Router has been configured to support External Coprocessing.
2. Router has been configured to send request bodies to coprocessors. This is a non-default configuration and must be configured intentionally by administrators.

You can identify if you are impacted by reviewing your router’s configuration YAML for the following config:

...
coprocessor:
  url: http://localhost:9000 # likely different in your environment
  router:
    request:
      body: true # this must be set to 'true' to be impacted
...

External Coprocessing was initially made available as an experimental feature with Router version 1.21.0 on 2023-06-20 and was made generally available with Router version 1.38.0 on 2024-01-19. More information about the Router’s External Coprocessing feature is available here.

When using Native Rust Plugins:

Instances of the Apollo Router running versions >=1.7.0 and <1.52.1 are impacted by a denial-of-service vulnerability if all of the following are true:

1. Router has been configured to use a custom-developed Native Rust Plugin
2. The plugin accesses Request.router_request in the RouterService layer
3. You are accumulating the body from Request.router_request into memory

To use a plugin, you need to be running a customized Router binary. Additionally, you need to have a plugins section with at least one plugin defined in your Router’s configuration YAML. That plugin would also need to define a custom router_service method.

You can check for a defined plugin by reviewing for the following in your Router’s configuration YAML:

...
plugins:
    custom_plugin_name:
        # custom config here
...

You can check for a custom router_service method in a plugin, by reviewing for the following function signature in your plugin’s source:

fn router_service(&self, service: router::BoxService) -> router::BoxService

More information about the Router’s Native Rust Plugin feature is available here.

Impact Detail

If using an impacted configuration, the Router will load entire HTTP request bodies into memory without respect to other HTTP request size-limiting configurations like limits.http_max_request_bytes. This can cause the Router to be out-of-memory (OOM) terminated if a sufficiently large request is sent to the Router.

By default, the Router sets limits.http_max_request_bytes to 2 MB. More information about the Router’s request limiting features is available here.

Patches

Apollo Router 1.52.1

If you have an impacted configuration as defined above, please upgrade to at least Apollo Router 1.52.1.

Workarounds

If you cannot upgrade, you can mitigate the denial-of-service opportunity impacting External Coprocessors by setting the coprocessor.router.request.body configuration option to false. Please note that changing this configuration option will change the information sent to any coprocessors you have configured and may impact functionality implemented by those coprocessors.

If you have developed a Native Rust Plugin and cannot upgrade, you can update your plugin to either not accumulate the request body or enforce a maximum body size limit.

You can also mitigate this issue by limiting HTTP body payload sizes prior to the Router (e.g., in a proxy or web application firewall appliance).

References

Apollo Router 1.52.1 Release Notes
External Coprocessing documentation
HTTP Request Limiting documentation
Native Rust Plugin documentation