---
id: CVE-2026-47074
title: >-
  Hackney: Per-chunk timeout with unbounded body accumulation enables slow-drip
  OOM
summary: >-
  Hackney: Per-chunk timeout with unbounded body accumulation enables slow-drip
  OOM
severity: high
cwe:
  - CWE-295
  - CWE-400
vendor: hackney
product: hackney
ecosystem: erlang
affected:
  - 'hackney >= 4.0.0, < 4.0.1'
patched:
  - hackney 4.0.1
published: '2026-06-26'
updated: '2026-06-26'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-jq4m-q6p2-8gwc'
references:
  - url: 'https://github.com/benoitc/hackney/security/advisories/GHSA-jq4m-q6p2-8gwc'
  - url: >-
      https://github.com/ex-aws/ex_aws_sns/security/advisories/GHSA-8jgf-23q5-x7xx
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-47074'
  - url: >-
      https://github.com/ex-aws/ex_aws_sns/commit/1853d280b152d10384a1e21a22cf22152a60be48
  - url: 'https://cna.erlef.org/cves/CVE-2026-47074.html'
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-47074'
  - url: 'https://github.com/advisories/GHSA-jq4m-q6p2-8gwc'
tags:
  - ghsa
  - erlang
epss: 0.00377
epssPercentile: 0.28964
ingestedAt: '2026-06-29T13:24:35.109Z'
---

## Overview

### Summary

`hackney_h3:await_response_loop/6` in `src/hackney_h3.erl` accumulates the HTTP/3 response body in memory without any size cap. The `after Timeout` clause is a per-message inactivity timer, not a wall-clock deadline: every received `stream_data` chunk, housekeeping `select` message, or `settings` frame resets it. A malicious HTTP/3 server that drips one small chunk every `Timeout - 1` ms with `Fin = false` and never terminates the stream keeps the loop alive indefinitely while the accumulation buffer grows without bound, eventually exhausting the BEAM process heap.

### Details

In `src/hackney_h3.erl`, `await_response_loop/6` (line 430) builds the body with:

```erlang
NewBody = <<AccBody/binary, Data/binary>>
```

There is no `max_body` check and no monotonic deadline. The `after Timeout` clause at line 463 is restarted on each loop iteration. A server that ensures at least one message arrives within `Timeout` ms indefinitely (one small chunk per interval is sufficient) prevents the timeout from firing while `AccBody` grows linearly. The same module's `wait_connected/3` (lines 388-389) shows the correct pattern: track an absolute start time and pass a shrinking `Remaining` budget into each `receive`. This loop does not.

### Configurations

Only the HTTP/3 transport is affected. Applications using the default TCP/TLS hackney transport are not vulnerable. The vulnerability requires using `hackney_h3` directly or passing `{transport, h3}` to `hackney:request/5`.

### PoC

1. Stand up an HTTP/3 server that responds with `200 OK` headers (`Fin = false`), then emits a small `stream_data` chunk every `Timeout - margin` ms with `Fin = false` indefinitely.
2. Issue `hackney:request(get, Url, [], <<>>, [{transport, h3}])` against it.
3. Watch the client process heap grow monotonically. The configured timeout never fires; the process is eventually killed by `max_heap_size` or the OS OOM killer.

### Impact

Remote denial of service via unbounded memory consumption. Affects hackney 2.0.0 through 4.0.0 when using the HTTP/3 transport against an attacker-controlled or attacker-influenced server. Each affected request consumes unbounded memory until the BEAM is killed. CVSS v4.0: **8.2 (HIGH)**.

## Resources

* Introduction commit: https://github.com/benoitc/hackney/commit/0334af206d5099fdf510ed9eda18e34396f065ad
* Patch commit: https://github.com/benoitc/hackney/commit/3d25f9fea26c90609de9d64366fedfe5065413bc

## Affected packages

- `hackney >= 4.0.0, < 4.0.1`

## Remediation

Upgrade to a patched release:

- `hackney 4.0.1`