OutOfMemoryError for large multipart without filename in Eclipse Jetty

Impact

Servlets with multipart support (e.g. annotated with @MultipartConfig) that call HttpServletRequest.getParameter() or HttpServletRequest.getParts() may cause OutOfMemoryError when the client sends a multipart request with a part that has a name but no filename and a very large content.

This happens even with the default settings of fileSizeThreshold=0 which should stream the whole part content to disk.

An attacker client may send a large multipart request and cause the server to throw OutOfMemoryError.
However, the server may be able to recover after the OutOfMemoryError and continue its service – although it may take some time.

A very large number of parts may cause the same problem.

Patches

Patched in Jetty versions

• 9.4.51.v20230217 - via PR #9345
• 10.0.14 - via PR #9344
• 11.0.14 - via PR #9344

Workarounds

Multipart parameter maxRequestSize must be set to a non-negative value, so the whole multipart content is limited (although still read into memory).
Limiting multipart parameter maxFileSize won’t be enough because an attacker can send a large number of parts that summed up will cause memory issues.

References

• https://github.com/eclipse/jetty.project/issues/9076
• https://github.com/jakartaee/servlet/blob/6.0.0/spec/src/main/asciidoc/servlet-spec-body.adoc#32-file-upload