CVE-2026-56139: Apache Camel: Camel-Undertow: The muteException consumer option defaulted to false, so a processing error returned the full Java stack trace in the HTTP response body, disclosing sensitive internal information to unauthenticated clients - and the option was not honoured

[Andrea Cosentino <acosentino () apache org>]

Severity: moderate 

Affected versions:

- Apache Camel (org.apache.camel:camel-undertow) 4.0.0 before 4.14.8
- Apache Camel (org.apache.camel:camel-undertow) 4.15.0 before 4.18.3
- Apache Camel (org.apache.camel:camel-undertow) 4.19.0 before 4.21.0

Description:

Generation of Error Message Containing Sensitive Information vulnerability in Apache Camel Undertow Component.

The camel-undertow HTTP server consumer exposes a muteException option that controls what is returned to the client 
when a route processing error occurs. This option defaulted to false, whereas the other Camel HTTP server components 
(camel-http / camel-jetty / camel-servlet and camel-platform-http) default it to true. With muteException=false, when a 
request triggers an exception during route processing the consumer writes the full Throwable stack trace into the HTTP 
response body as text/plain instead of returning an empty body. Any unauthenticated client that can reach the endpoint 
and cause a processing error - for example by sending a malformed request body, an invalid parameter, or otherwise 
triggering a route-internal failure - therefore receives a complete Java stack trace. Such a stack trace can disclose 
sensitive internal information, including credentials embedded in exception messages, internal host names and IP 
addresses, filesystem paths, dependency and version details, database and class names, and the application's internal 
structure, which an attacker can use to plan further attacks. In addition, for Rest DSL consumers the muteException 
option was not honoured at all: the RestUndertowHttpBinding was created with a hard-coded false, so the stack trace was 
returned even when muteException=true had been configured.
This issue affects Apache Camel: from 4.0.0 before 4.14.8, from 4.15.0 before 4.18.3, from 4.19.0 before 4.21.0.

Users are recommended to upgrade to version 4.21.0, which fixes the issue. If users are on the 4.14.x LTS releases 
stream, then they are suggested to upgrade to 4.14.8. If users are on the 4.18.x releases stream, then they are 
suggested to upgrade to 4.18.3. For deployments that cannot upgrade immediately, set muteException=true explicitly on 
the camel-undertow consumer (for example undertow: http://0.0.0.0:8080/api?muteException=true , or globally via the 
camel.component.undertow.mute-exception=true property), so that processing errors no longer return the stack trace to 
the client; note that on affected releases this workaround does not cover Rest DSL consumers, whose binding ignores the 
option until the fix is applied.

Credit:

Yu Bao from PayPal (finder)
Andrea Cosentino (remediation developer)

References:

https://camel.apache.org/security/CVE-2026-56139.html
https://camel.apache.org/
https://www.cve.org/CVERecord?id=CVE-2026-56139