Impact

By using an invalid transfer-encoding header, an attacker could smuggle an HTTP response.

Originally reported by @ZeddYu, who has our thanks for the detailed report.

Patches

The problem has been fixed in Puma 3.12.5 and Puma 4.3.4.

For more information

If you have any questions or comments about this advisory:

• Open an issue in Puma
• See our security policy