wojtekmach req up to 0.6.0 lib/req/steps.ex data amplification

Summaryinfo

A vulnerability marked as problematic has been reported in wojtekmach req up to 0.6.0. The impacted element is an unknown function in the library lib/req/steps.ex. The manipulation leads to data amplification. This vulnerability is listed as CVE-2026-49755. The attack may be initiated remotely. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in wojtekmach req up to 0.6.0. It has been rated as problematic. This issue affects an unknown code in the library lib/req/steps.ex. The manipulation with an unknown input leads to a data amplification vulnerability. Using CWE to declare the problem leads to CWE-409. The product does not handle or incorrectly handles a compressed input with a very high compression ratio that produces a large output. Impacted is availability. The summary by CVE is:

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.

The weakness was presented by Peter Ullrich and Jonatan Männchen. The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-49755 since 06/01/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

Upgrading to version 0.6.1 eliminates this vulnerability. Applying the patch 84977e5b1a83f26e749d55ad06e3625464af4e8d is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-35098). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Vendor

• wojtekmach

Name

• req

Version

• 0.1
• 0.2
• 0.3
• 0.4
• 0.5
• 0.6.0

Website

• Product: https://github.com/wojtekmach/req/

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Discussion