CVE-2026-111101: HTTP/1.1 chunked request bodies made of 1-byte chunks amplify memory use in Bandit

Q: Which deployments are exposed to this issue?

Bandit versions from 0.1.0 before 1.14.0 are affected. Any server accepting HTTP/1.1 requests with chunked bodies can be targeted, including routes that do not explicitly read request bodies.

Q: What does an attacker need to do to trigger the resource exhaustion?

An unauthenticated remote attacker can send an HTTP/1.1 chunked request body containing a very large number of 1-byte chunks. Keep-alive connections can trigger the vulnerable body-draining path even when the application route does not consume the body.

Q: Why does limiting read_body/2 length not prevent this?

The :length option counts payload bytes, not the number of chunks or their per-chunk memory overhead. Each tiny chunk is retained as a separate list cell and binary term until the body is joined, allowing memory use to greatly exceed the actual body size.

Published Oct 26, 2026

Updated

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.iodatatobinary/1 joins them, and nothing limits the number of chunks. The :length option of readbody/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 ensurecompleted/1 drains unread bodies through the same reader.

This issue affects bandit: from 0.1.0 before 1.14.0.

Affected Software

1 affected component

hex/bandit>=0.1.0<1.14.0

Event History

Oct 26, 2026

CVE Published

via MITRE·01:31 PM

Data Sourced

via MITRE·01:31 PM

DescriptionWeakness

Frequently Asked Questions

Which deployments are exposed to this issue?

Bandit versions from 0.1.0 before 1.14.0 are affected. Any server accepting HTTP/1.1 requests with chunked bodies can be targeted, including routes that do not explicitly read request bodies.

What does an attacker need to do to trigger the resource exhaustion?

An unauthenticated remote attacker can send an HTTP/1.1 chunked request body containing a very large number of 1-byte chunks. Keep-alive connections can trigger the vulnerable body-draining path even when the application route does not consume the body.

Why does limiting read_body/2 length not prevent this?

The :length option counts payload bytes, not the number of chunks or their per-chunk memory overhead. Each tiny chunk is retained as a separate list cell and binary term until the body is joined, allowing memory use to greatly exceed the actual body size.

CVE-2026-111101: HTTP/1.1 chunked request bodies made of 1-byte chunks amplify memory use in Bandit

Affected Software

Event History

Frequently Asked Questions

Which deployments are exposed to this issue?

What does an attacker need to do to trigger the resource exhaustion?

Why does limiting read_body/2 length not prevent this?

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Frequently Asked Questions

Which deployments are exposed to this issue?

What does an attacker need to do to trigger the resource exhaustion?

Why does limiting read_body/2 length not prevent this?