# CVE-2026-47077: Unbounded body accumulation in HTTP/3 response loop in hackney

> A malicious HTTP/3 server can cause an out-of-memory denial of service in the hackney library by sending slow, unbounded response chunks.

- **Severity:** High 8.2 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 May 2026
- **Updated:** 27 May 2026
- **Also known as:** EEF-CVE-2026-47077, GHSA-jq4m-q6p2-8gwc

## What is CVE-2026-47077?

CVE-2026-47077 is a high-severity denial of service vulnerability in benoitc hackney, published on 25 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Allocation of Resources Without Limits or Throttling vulnerability in benoitc hackney allows Flooding. hackney_h3:await_response_loop/6 accumulates the HTTP/3 response body in memory without any size cap. The after Timeout clause is a per-message inactivity timer that resets on every received chunk, housekeeping message, or settings frame — it is not a wall-clock deadline. A malicious HTTP/3 server that emits one small chunk every Timeout - 1 ms with Fin = false and never sends a final frame keeps the loop alive indefinitely while the accumulation buffer grows linearly without bound, eventually exhausting the BEAM process heap and causing an out-of-memory condition.

This issue affects hackney: from 2.0.0 before 4.0.1.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-47077?

3 open source packages ship an affected version, including hackney. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `hackney` | Hex | From 2.0.0 | 4.0.1 |
| `hackney` | Hex | From 2.0.0 | 4.0.1 |
| `hackney` | Hex | From 2.0.0 | 4.0.1 |

Products: Benoitc Hackney.

## How do I fix CVE-2026-47077?

Upgrade hackney to 4.0.1 or later.

## Is CVE-2026-47077 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-47077 exists.

## Other vulnerabilities in benoitc hackney

- [CVE-2026-47066](https://insights.sbomify.com/CVE-2026-47066/): Infinite loop in Alt-Svc header parser in hackney (high 8.7)
- [CVE-2026-47067](https://insights.sbomify.com/CVE-2026-47067/): Atom table exhaustion via unrecognized URL schemes in hackney (high 8.7)
- [CVE-2026-47073](https://insights.sbomify.com/CVE-2026-47073/): Unbounded memory consumption in WebSocket client in hackney (high 8.7)
- [CVE-2026-47071](https://insights.sbomify.com/CVE-2026-47071/): SOCKS5 TLS upgrade ignores caller timeout in hackney (high 8.2)
- [CVE-2026-47072](https://insights.sbomify.com/CVE-2026-47072/): CRLF injection in WebSocket upgrade request in hackney (medium 6.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-47077 and fix it if it is affected.

What it is: CVE-2026-47077 is a high-severity denial of service vulnerability in benoitc hackney, published on 25 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-47077 exists.

Affected packages and fixed versions:
- hackney (Hex): affected from 2.0.0; fixed in 4.0.1
- hackney (Hex): affected from 2.0.0; fixed in 4.0.1
- hackney (Hex): affected from 2.0.0; fixed in 4.0.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-47077/ (Markdown: https://insights.sbomify.com/CVE-2026-47077/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-47077
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-47077
- OSV: https://osv.dev/vulnerability/CVE-2026-47077

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-47077/
Summaries are generated and may contain mistakes; the official description above is the record.