CVE-2026-1526

The undici WebSocket client is vulnerable to a denial-of-service attack via unbounded memory consumption during permessage-deflate decompression. When a WebSocket connection negotiates the permessage-deflate extension, the client decompresses incoming compressed frames without enforcing any limit on the decompressed data size. A malicious WebSocket server can send a small compressed frame (a "decompression bomb") that expands to an extremely large size in memory, causing the Node.js process to exhaust available memory and crash or become unresponsive. The vulnerability exists in the PerMessageDeflate.decompress() method, which accumulates all decompressed chunks in memory and concatenates them into a single Buffer without checking whether the total size exceeds a safe threshold.

The undici WebSocket client is vulnerable to a denial-of-service attack via unbounded memory consumption during permessage-deflate decompression. When a WebSocket connection negotiates the permessage-deflate extension, the client decompresses incoming compressed frames without enforcing any limit on the decompressed data size. A malicious WebSocket server can send a small compressed frame (a "decompression bomb") that expands to an extremely large size in memory, causing the Node.js process to exhaust available memory and crash or become unresponsive. The vulnerability exists in the PerMessageDeflate.decompress() method, which accumulates all decompressed chunks in memory and concatenates them into a single Buffer without checking whether the total size exceeds a safe threshold.

## Description The undici WebSocket client is vulnerable to a denial-of-service attack via unbounded memory consumption during permessage-deflate decompression. When a WebSocket connection negotiates the permessage-deflate extension, the client decompresses incoming compressed frames without enforcing any limit on the decompressed data size. A malicious WebSocket server can send a small compressed frame (a "decompression bomb") that expands to an extremely large size in memory, causing the Node.js process to exhaust available memory and crash or become unresponsive. The vulnerability exists in the `PerMessageDeflate.decompress()` method, which accumulates all decompressed chunks in memory and concatenates them into a single Buffer without checking whether the total size exceeds a safe threshold. ## Impact - Remote denial of service against any Node.js application using undici's WebSocket client - A single compressed WebSocket frame of ~6 MB can decompress to ~1 GB or more - Memory exhaustion occurs in native/external memory, bypassing V8 heap limits - No application-level mitigation is possible as decompression occurs before message delivery ### Patches Users should upgrade to fixed versions. ### Workarounds No workaround are possible.

## Description The undici WebSocket client is vulnerable to a denial-of-service attack via unbounded memory consumption during permessage-deflate decompression. When a WebSocket connection negotiates the permessage-deflate extension, the client decompresses incoming compressed frames without enforcing any limit on the decompressed data size. A malicious WebSocket server can send a small compressed frame (a "decompression bomb") that expands to an extremely large size in memory, causing the Node.js process to exhaust available memory and crash or become unresponsive. The vulnerability exists in the `PerMessageDeflate.decompress()` method, which accumulates all decompressed chunks in memory and concatenates them into a single Buffer without checking whether the total size exceeds a safe threshold. ## Impact - Remote denial of service against any Node.js application using undici's WebSocket client - A single compressed WebSocket frame of ~6 MB can decompress to ~1 GB or more - Memory exhaustion occurs in native/external memory, bypassing V8 heap limits - No application-level mitigation is possible as decompression occurs before message delivery ### Patches Users should upgrade to fixed versions. ### Workarounds No workaround are possible.

El cliente WebSocket undici es vulnerable a un ataque de denegación de servicio a través de un consumo de memoria ilimitado durante la descompresión permessage-deflate. Cuando una conexión WebSocket negocia la extensión permessage-deflate, el cliente descomprime las tramas comprimidas entrantes sin imponer ningún límite en el tamaño de los datos descomprimidos. Un servidor WebSocket malicioso puede enviar una pequeña trama comprimida (una 'bomba de descompresión') que se expande a un tamaño extremadamente grande en memoria, causando que el proceso de Node.js agote la memoria disponible y colapse o deje de responder. La vulnerabilidad existe en el método PerMessageDeflate.decompress(), que acumula todos los fragmentos descomprimidos en memoria y los concatena en un único Buffer sin verificar si el tamaño total excede un umbral seguro.