HTTP/1.1 chunked request bodies made of 1-byte chunks amplify memory use in Bandit

Overview

Allocation of Resources Without Limits or Throttling vulnerability in the HTTP/1.1 chunked body reader of mtrudel bandit allows an unauthenticated remote attacker to exhaust server memory and CPU via a request body made of many 1-byte chunks.

The chunked reader in lib/bandit/http1/socket.ex keeps every chunk as its own list cell and binary term until IO.iodata_to_binary/1 joins them, and nothing limits the number of chunks. The :length option of read_body/2 counts only data bytes, so tiny chunks cost far more memory than their payload: 48 MB of 1-byte chunks grew one handler process to about 500 MB and took about 6 s of CPU. The route does not need to read the body, because on keep-alive connections ensure_completed/1 drains unread bodies through the same reader.

This issue affects bandit: from 0.1.0 before 1.14.0.

Affected

• bandit >= 0.1.0 < 1.14.0
• mtrudel/bandit >= 7201270c34b90f6c9e15c0386c2bb802c0c72ab4 < 220b9dfd27f9a21305be2afc75cbe585ddc24e7a

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Workarounds

From 0.7.0, a server whose clients and proxies all speak HTTP/2 can disable HTTP/1 with http_1_options: [enabled: false], so that the vulnerable chunked body reader never runs.