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# COMPASS SECURITY ADVISORY
# https://www.compass-security.com/research/advisories/
#
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#
# Product:   Vert.x [1]
# CSNC ID:   CSNC-2018-021
# Subject:   HTTP Header Injection
# Risk:      Medium
# Effect:    Remotely exploitable
# Author:    Lukasz D. (advisories@compass-security.com)
# Date:      12.06.2018
#
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Introduction:
-------------
Eclipse Vert.x is a tool-kit for building reactive applications on the JVM.
Vert.x can be used for simple network utilities, sophisticated modern web
applications, HTTP/REST microservices, high volume event processing
or a full-blown back-end message-bus applications. Vert.x is used by many
different companies from real-time gaming to banking and everything in between.

Vert.x does not filter carriage return and line feed characters from values of
set HTTP response headers. This allows to manipulate values of the set HTTP
headers and to add arbitrary new headers. In particular, issuing a redirection
and manipulation of cookies set by the server is possible.

Affected:
---------
The following Vert.x versions are vulnerable:
- 3.0.0 - 3.5.1

Technical Description:
----------------------
The method putHeader(String name, String value) used to set new headers in the
HTTP response does not filter carriage return and line feed characters from
the header value. If a web application uses a user-provided parameter as
a value of the header, then it is possible for a user to add new HTTP headers
of his choice.

For example, a Vert.x-based web application may use the vulnerable method like
this: putHeader("User-Header", foo), where foo is the user-provided parameter.

Then:
    Requesting /vulnerable?foo=bar will add a header: "User-Header: bar".
    Requesting /vulnerable?foo=bar%0D%0ASet-Cookie:%20mycookie=hello will add
        a header: "User-Header: bar" and additionally will set a new cookie
        with name "mycookie" and value "hello".

Workaround / Fix:
-----------------
It needs to be ensured that every header value which is set based on
a user-provided parameter does not contain carriage return and line feed
characters.

Timeline:
---------
2018-02-22:   Vulnerability discovered
2018-04-04:   Initial vendor notification
2018-04-04:   Initial vendor response
2018-06-04:   Patched version released
2018-06-13:   Public disclosure

References:
-----------
[1]: https://vertx.io/