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.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| wojtekmach | req | unaffected |
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| wojtekmach | req | unaffected |
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No advisories yet.
Solution
No solution given by the vendor.
Workaround
Disable Req's automatic body decoding on requests that fetch attacker-influenced URLs by passing decode_body: false to Req.new/1 / Req.get!/1. To also skip the content-encoding decompression pipeline, pass raw: true. Both options leave the response body as the raw on-the-wire bytes, so the caller can size-check before any decompression.
Mon, 08 Jun 2026 17:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Metrics |
ssvc
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Mon, 08 Jun 2026 15:45:00 +0000
| Type | Values Removed | Values Added |
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| 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. | |
| Title | Decompression bomb DoS in Req via auto-decoded archive and compressed response bodies | |
| First Time appeared |
Wojtekmach
Wojtekmach req |
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| Weaknesses | CWE-409 | |
| CPEs | cpe:2.3:a:wojtekmach:req:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Wojtekmach
Wojtekmach req |
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| References |
| |
| Metrics |
cvssV4_0
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Projects
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MITRE
Status: PUBLISHED
Assigner: EEF
Published:
Updated: 2026-06-08T16:50:03.277Z
Reserved: 2026-06-01T13:45:22.448Z
Link: CVE-2026-49755
Vulnrichment
Updated: 2026-06-08T16:49:41.908Z
NVD
Status : Received
Published: 2026-06-08T16:16:43.860
Modified: 2026-06-08T17:16:52.627
Link: CVE-2026-49755
Redhat
No data.
OpenCVE Enrichment
Updated: 2026-06-08T16:45:26Z