Racket Web Server Security Vulnerability

We recently discovered a serious security vulnerability in the Racket web server, which can lead to unintended disclosure of files on the machine running the web server. This vulnerability is fixed in Racket version 6.4, just released, and we encourage people to upgrade to that version.

The vulnerability affects web servers that serve static files using the #:extra-files-paths option, including the default value of this option. If you do not use the Racket web serve to serve static files, or you do so via a mechanism that does not use the make-url->path function, then you are likely not vulnerable. Affected web serves will allow specially-crafted URLs to access files outside of the specified paths, potentially exposing any file that the web server process is able to read.

If you cannot immediately upgrade to version 6.4, we have provided a package catalog with updated versions of the "web-server-lib" package for versions of Racket back to 6.0. That catalog is located at

 http://download.racket-lang.org/patches/web-server-1/

To use it to upgrade your Racket installation, add it as a catalog using raco pkg config. To make this process easier, you can download the Racket script available here. Then run:

  $ racket add-catalog.rkt
  $ raco pkg update -i web-server-lib

If you need advice on updating Racket installations older than version 6.0, please let us know and we will provide them.

To test that your Racket installation is fixed, you can run the program here. It will print whether your installation is out of date.

Racket v6.4

Racket version 6.4 is now available from http://racket-lang.org/

• We fixed a security vulnerability in the web server. The existing web server is vulnerable to a navigation attack if it is also enabled to serve files statically; that is, any file readable by the web server is accessible remotely. For more information, see this post.
• DrRacket's scrolling is faster.
• Incremental garbage-collection mode can eliminate long pauses in a program. For example, incremental mode is useful for avoiding pauses in games and animations.
  Programs must specifically request incremental mode with (collect-garbage 'incremental), but libraries such as 2htdp/universe include the request as part of the library's implementation.
• The default package catalog is an HTTPS address instead of HTTP, and package operations properly validate server certificates when using HTTPS.
• Documentation may define their own categories for the manual top-level page by using strings, rather than only symbols that name pre-defined categories.
• The Racket cheat sheet is included in the main distribution.
• DrRacket is available in Bulgarian, thanks to Alexander Shopov.
• The contract Typed Racket generates for the Any type is more permissive, allowing more typed/untyped programs to work without contract errors.
• Redex supports binding specifications; describe which variables bind in which expressions and your metafunctions and reduction relations automatically become scope-sensitive. Thanks to Paul Stansifer for this improvement.
• All pict functions accept pict-convertibles. This allows for transparent interoperability between pict and libraries like 2htdp/image.
• The raco profile and raco contract-profile commands provide easy access to profiling tools, without requiring program modifications.

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