Impact

ActionController::Live::Buffer#close pushes its end-of-stream marker onto the response's bounded queue while it holds the buffer's monitor. When the client has stopped reading and the queue is full, the push blocks, and Buffer#abort, which runs when the client disconnects or a write times out, waits indefinitely for the same monitor. Each such response could permanently hold a web server thread and its ActionController::Live thread, possibly resulting in a DoS vulnerability through thread exhaustion.

Applications that stream responses with ActionController::Live, including send_stream, are affected. Applications that serve large files through Active Storage proxy mode are exposed to unauthenticated clients.

Releases

The fixed releases are available at the normal locations.

Patches for those who cannot upgrade at once:

• 8.1: https://github.com/rails/rails/commit/ccbfc09690fef05fdd2a9969c917a71b92cc98fc.patch
• 8.0: https://github.com/rails/rails/commit/27ad18ed5900dee28ba20e9c6fc718ff751fa215.patch

Credit

This issue was found by the Anthropic OSS Scanner (ANT-2026-LDFW5N2T).