CVE-2026-49755

Estado: AnalizadaAlta (8.2)—

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.

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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.

CVSS

Versión: 4.0
Vector: 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Puntuación base: 8.2

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.70%
Percentil entre todas las CVEs puntuadas: 52
Fecha de la puntuación: 6/10/2026

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

ExplotaciónT1190 Exploit Public-Facing Applicationinitial access85 %
Impacto principalT1499.004 Application or System Exploitationimpact90 %
Impacto secundarioT1565.001 Stored Data Manipulationimpact60 %

Servidor HTTP controlado por atacante explota decompresión sin límites en cliente Req remoto (AV:N, PR:N). Compresión en cascada causa DoS por agotamiento de memoria (data amplification attack).

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Filter Network Traffic Vulnerability Scanning Restrict File and Directory Permissions Privileged Account Management Remote Data Storage Network Segmentation

Tecnologías afectadas (1)

Wojtekmach — REQ

CWE

CWE-409

Referencias

JSON original (NVD)

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      "value": "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.\n\nReq'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.\n\nBoth 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.\n\nThis issue affects req: from 0.1.0 before 0.6.1."
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      "value": "La vulnerabilidad de manejo inadecuado de datos altamente comprimidos (amplificación de datos) en wojtekmach Req permite a los servidores HTTP controlados por el atacante agotar la memoria en un cliente Req mediante cuerpos de respuesta de bomba de descompresión.\n\nLa pipeline de respuesta predeterminada de Req incluye Req.Steps.decode_body/1 y Req.Steps.decompress_body/1 en lib/req/steps.ex. decode_body/1 despacha según el content-type proporcionado por el servidor (o extensión de URL) y llama a :zip.extract(body, [:memory]) para application/zip, a :erl_tar.extract({:binary, body}, [:memory]) para application/x-tar, y a :erl_tar.extract({:binary, body}, [:memory, :compressed]) para application/gzip / .tgz. Cada uno devuelve el contenido completo del archivo descomprimido como una lista [{name, bytes}] en memoria, sin límite de tamaño por entrada o total. decompress_body/1 recorre el encabezado content-encoding y encadena decodificadores :zlib/:brotli/:ezstd, por lo que una respuesta que anuncia content-encoding: gzip, gzip, gzip se infla a través de múltiples capas sin límite.\n\nAmbos pasos están habilitados por defecto, no se requiere la participación del llamador, y el atacante controla los encabezados content-type y content-encoding en su propio servidor (o en cualquier host alcanzado a través del seguimiento automático de redirecciones de Req). Una respuesta de menos de un megabyte puede expandirse a múltiples gigabytes en la víctima, colapsando el proceso BEAM.\n\nEste problema afecta a req: desde 0.1.0 antes de 0.6.1."
    }
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  "lastModified": "2026-08-18T15:46:34.387",
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