# CVE-2026-49755: Decompression bomb DoS in Req via auto-decoded archive and compressed response bodies

> An attacker-controlled HTTP server can cause memory exhaustion and crash the Req client by sending decompression bomb responses.

- **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:** 8 Jun 2026
- **Updated:** 8 Jun 2026
- **Also known as:** EEF-CVE-2026-49755, GHSA-655f-mp8p-96gv

## What is CVE-2026-49755?

CVE-2026-49755 is a high-severity denial of service vulnerability in wojtekmach req, published on 8 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in wojtekmach Req allows attacker-controlled HTTP servers to exhaust memory in a Req client via decompression-bomb response bodies.

Req's default response pipeline includes Req.Steps.decode_body/1 and Req.Steps.decompress_body/1 in lib/req/steps.ex. decode_body/1 dispatches on the server-supplied content-type (or URL extension) and calls :zip.extract(body, [:memory]) for application/zip, :erl_tar.extract({:binary, body}, [:memory]) for application/x-tar, and :erl_tar.extract({:binary, body}, [:memory, :compressed]) for application/gzip / .tgz. Each returns the full decompressed archive contents as a [{name, bytes}] list in memory, with no per-entry or total size cap. decompress_body/1 walks the content-encoding header and chains :zlib/:brotli/:ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip inflates through multiple layers without bound.

Both steps are enabled by default, no caller opt-in is required, and the attacker controls the content-type and content-encoding headers on their own server (or on any host reached via Req's automatic redirect following). A sub-megabyte response can expand to multiple gigabytes on the victim, crashing the BEAM process.

This issue affects req: from 0.1.0 before 0.6.1.

Weakness: CWE-409 (Improper Handling of Highly Compressed Data (Data Amplification))

## Which versions are affected by CVE-2026-49755?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `req` | Hex | From 0.1.0 | 0.6.1 |
| `req` | Hex | From 0.1.0 | 0.6.1 |
| `req` | Hex | From 0.1.0 | 0.6.1 |

Products: Wojtekmach Req.

## How do I fix CVE-2026-49755?

Upgrade req to 0.6.1 or later.

## Is CVE-2026-49755 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49755 exists.

## Other vulnerabilities in wojtekmach req

- [CVE-2026-49756](https://insights.sbomify.com/CVE-2026-49756/): Multipart form-data header injection in Req via unescaped name/filename/content_type (low 2.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-49755 and fix it if it is affected.

What it is: CVE-2026-49755 is a high-severity denial of service vulnerability in wojtekmach req, published on 8 Jun 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-2026-49755 exists.

Affected packages and fixed versions:
- req (Hex): affected from 0.1.0; fixed in 0.6.1
- req (Hex): affected from 0.1.0; fixed in 0.6.1
- req (Hex): affected from 0.1.0; fixed in 0.6.1

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-2026-49755/ (Markdown: https://insights.sbomify.com/CVE-2026-49755/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-49755
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-49755
- OSV: https://osv.dev/vulnerability/CVE-2026-49755

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-49755/
Summaries are generated and may contain mistakes; the official description above is the record.