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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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
Which versions are affected by CVE-2026-49755?
3 open source packages ship an affected version, including req. It affects 1 product.
| Package | 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 include Wojtekmach Req.
How do I fix CVE-2026-49755?
Upgrade req to 0.6.1 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
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
Sources
Also known as EEF-CVE-2026-49755, GHSA-655f-mp8p-96gv.