Apache Camel: dynamic-router control messages let senders run arbitrary expressions

Improper Control of Generation of Code ('Code Injection'), Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection') vulnerability in Apache Camel.

This issue affects Apache Camel: from 4.4.0 before 4.18.5, from 4.19.0 before 4.22.1.

The dynamic-router-control endpoint, introduced in 4.4.0, lets routing participants manage Dynamic Router subscriptions by sending control messages. When it handled a subscribe or update request, DynamicRouterControlProducer took the subscription predicate and the name of the language used to compile it from the incoming message, either from the predicate and expressionLanguage fields of a DynamicRouterControlMessage body or from the CamelDynamicRouterPredicate and CamelDynamicRouterExpressionLanguage headers. DynamicRouterControlService then resolved that language from the CamelContext and compiled the expression into a Predicate, with no allow-list and no opt-in. The compiled predicate was added to the channel's rule base and evaluated against every exchange routed through the corresponding dynamic-router endpoint for as long as the subscription existed. A route that forwards messages from an external transport to the control endpoint, as shown in the component documentation for routing participants in other JVMs or applications, therefore let any actor able to send a message on that transport supply an expression of their choosing, which was evaluated with the privileges of the Camel process. Any expression language available on the classpath could be selected, including the simple language, which is always present and was the default on the header path, so removing optional expression languages from the classpath did not prevent the issue. Exploitation requires the ability to send a message on a transport whose route forwards it to a dynamic-router-control endpoint; no other authentication or user interaction is needed. Releases before 4.4.0 are not affected, because their control channel took predicate expressions only from the endpoint URI configured by the route author.

Users are recommended to upgrade to version 4.23.0, which fixes the issue. If users are on the 4.22.x releases stream, then they are suggested to upgrade to 4.22.1. If users are on the 4.18.x releases stream, then they are suggested to upgrade to 4.18.5. The 4.14.x releases stream and earlier reached end of life before this issue was resolved and will not receive a fix, so deployments on those lines must move to a supported release. After upgrading, a control message that carries a predicate expression or an expression language is rejected unless the new allowPredicateFromMessage option is enabled on the dynamic-router-control endpoint; enable it only when every sender of control messages is trusted. For deployments that cannot upgrade immediately, do not forward messages from untrusted or shared transports to a dynamic-router-control endpoint. Where control messages must cross such a transport, authenticate the sender and make sure the predicate and expression language of each subscription are set by the route rather than taken from the incoming message, for example by removing the CamelDynamicRouterPredicate and CamelDynamicRouterExpressionLanguage headers and clearing the predicate and expressionLanguage fields of a DynamicRouterControlMessage before it reaches the endpoint. Removing optional expression languages from the classpath is not a sufficient workaround. As defence in depth, restrict who can send to the transports that feed the control endpoint, and on 4.23.0 and 4.22.1 set the allowedSchemes option of the dynamic-router endpoint to limit which endpoints a subscription's destinationUri may name.