|[jetty-dev] Eclipse Jetty Too Large Headers|
Recently, a security issue was discovered that affects the specific Jetty versions 9.4.27.v20200227, 9.4.28.v20200408, and 9.4.29.v20200521. A CVE was filed for this issue.
When a specific response header has a value that is too long (for example in excess of 8KB of character data), Jetty will throw an exception to produce an HTTP 431 error. When this happens, the ByteBuffer containing the HTTP response headers is released back to the ByteBufferPool twice.
Because of this double release, two threads can acquire the same ByteBuffer from the pool and while thread1 is about to use the ByteBuffer to write response1 data, thread2 fills the ByteBuffer with response2 data. Thread1 then proceeds to write the buffer that now contains response2 data. This results in client1, which issued request1 and expects responses, to see response2 which could contain sensitive data belonging to client2 (HTTP session ids, authentication credentials, etc.).
It is important to note that an attack like this relies on a good deal of luck to garner information of any real value. There is no reliable way for an attacker to know what data will be dumped back, if any.
As for remediation, there are two choices. The easiest is simply to upgrade your version of Jetty to 9.4.30. The second option would be to set a relatively high response buffer header size to minimize any risk of encountering an attack such as this.
The Webtide Team
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