CVE-2017-16654: Intl bundle readers breaking out of paths

Affected versions

Symfony 2.7.0 to 2.7.37, 2.8.0 to 2.8.30, 3.2.0 to 3.2.13, and 3.3.0 to 3.3.12 versions of the Symfony Intl component are affected by this security issue.

The issue has been fixed in Symfony 2.7.38, 2.8.31, 3.2.14, 3.3.13, 3.4-BETA5, and 4.0-BETA5.

Note that no fixes are provided for Symfony 3.0 and 3.1 as they are not maintained anymore.

Description

The Intl component includes various bundle readers that are used to read resource bundles from the local filesystem. The read() methods of these classes use a path and a locale to determine the language bundle to retrieve.

The locale argument value is commonly retrieved from untrusted user input (like a URL parameter). An attacker can use this argument to navigate to arbitrary directories via the dot-dot-slash attack.

Resolution

The fix implements a check on the built filename to not break out of the path that was passed as an argument to the read() method.

The patch for this issue is available here.

Credits

I would like to thank David Bohannon for reporting this security issue, Christian Flothmann for providing a fix, and the Symfony Core Team for reviewing the patch.