CVE-2026-34941

Full vulnerability record from the local CVENow database.

Description

Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, Wasmtime contains a vulnerability where when transcoding a UTF-16 string to the latin1+utf16 component-model encoding it would incorrectly validate the byte length of the input string when performing a bounds check. Specifically the number of code units were checked instead of the byte length, which is twice the size of the code units. This vulnerability can cause the host to read beyond the end of a WebAssembly's linear memory in an attempt to transcode nonexistent bytes. In Wasmtime's default configuration this will read unmapped memory on a guard page, terminating the process with a segfault. Wasmtime can be configured, however, without guard pages which would mean that host memory beyond the end of linear memory may be read and interpreted as UTF-16. A host segfault is a denial-of-service vulnerability in Wasmtime, and possibly being able to read beyond the end of linear memory is additionally a vulnerability. Note that reading beyond the end of linear memory requires nonstandard configuration of Wasmtime, specifically with guard pages disabled. This vulnerability is fixed in 24.0.7, 36.0.7, 42.0.2, and 43.0.1.

Severity

MEDIUM

CVSS score

6.9 (v4.0)

Vulnerability status

Analyzed

Source identifier

[email protected]

Published

2026-04-09 19:16:23.693000

Last modified

2026-10-26 21:10:00.170000

View original CVE JSON

{
  "id": "CVE-2026-34941",
  "sourceIdentifier": "[email protected]",
  "published": "2026-04-09T19:16:23.693",
  "lastModified": "2026-10-26T21:10:00.170",
  "vulnStatus": "Analyzed",
  "cveTags": [],
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      "value": "Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, Wasmtime contains a vulnerability where when transcoding a UTF-16 string to the latin1+utf16 component-model encoding it would incorrectly validate the byte length of the input string when performing a bounds check. Specifically the number of code units were checked instead of the byte length, which is twice the size of the code units. This vulnerability can cause the host to read beyond the end of a WebAssembly's linear memory in an attempt to transcode nonexistent bytes. In Wasmtime's default configuration this will read unmapped memory on a guard page, terminating the process with a segfault. Wasmtime can be configured, however, without guard pages which would mean that host memory beyond the end of linear memory may be read and interpreted as UTF-16. A host segfault is a denial-of-service vulnerability in Wasmtime, and possibly being able to read beyond the end of linear memory is additionally a vulnerability. Note that reading beyond the end of linear memory requires nonstandard configuration of Wasmtime, specifically with guard pages disabled. This vulnerability is fixed in 24.0.7, 36.0.7, 42.0.2, and 43.0.1."
    },
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      "lang": "es",
      "value": "Wasmtime es un entorno de ejecución para WebAssembly. Antes de 24.0.7, 36.0.7, 42.0.2 y 43.0.1, Wasmtime contiene una vulnerabilidad donde al transcodificar una cadena UTF-16 a la codificación de modelo de componente latin1+utf16, validaría incorrectamente la longitud en bytes de la cadena de entrada al realizar una comprobación de límites. Específicamente, se comprobó el número de unidades de código en lugar de la longitud en bytes, que es el doble del tamaño de las unidades de código. Esta vulnerabilidad puede hacer que el host lea más allá del final de la memoria lineal de WebAssembly en un intento de transcodificar bytes inexistentes. En la configuración predeterminada de Wasmtime, esto leerá memoria no mapeada en una página de protección, terminando el proceso con un error de segmentación (segfault). Wasmtime puede configurarse, sin embargo, sin páginas de protección, lo que significaría que la memoria del host más allá del final de la memoria lineal podría leerse e interpretarse como UTF-16. Un error de segmentación del host es una vulnerabilidad de denegación de servicio en Wasmtime, y la posibilidad de leer más allá del final de la memoria lineal es adicionalmente una vulnerabilidad. Tenga en cuenta que leer más allá del final de la memoria lineal requiere una configuración no estándar de Wasmtime, específicamente con las páginas de protección deshabilitadas. Esta vulnerabilidad está corregida en 24.0.7, 36.0.7, 42.0.2 y 43.0.1."
    }
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  "references": [
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      "url": "https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-hx6p-xpx3-jvvv",
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}