CVE-2020-26237

Highlight.js is a syntax highlighter written in JavaScript. Highlight.js versions before 9.18.2 and 10.1.2 are vulnerable to Prototype Pollution. A malicious HTML code block can be crafted that will result in prototype pollution of the base object's prototype during highlighting. If you allow users to insert custom HTML code blocks into your page/app via parsing Markdown code blocks (or similar) and do not filter the language names the user can provide you may be vulnerable. The pollution should just be harmless data but this can cause problems for applications not expecting these properties to exist and can result in strange behavior or application crashes, i.e. a potential DOS vector. If your website or application does not render user provided data it should be unaffected. Versions 9.18.2 and 10.1.2 and newer include fixes for this vulnerability. If you are using version 7 or 8 you are encouraged to upgrade to a newer release.

Highlight.js is a syntax highlighter written in JavaScript. Highlight.js versions before 9.18.2 and 10.1.2 are vulnerable to Prototype Pollution. A malicious HTML code block can be crafted that will result in prototype pollution of the base object's prototype during highlighting. If you allow users to insert custom HTML code blocks into your page/app via parsing Markdown code blocks (or similar) and do not filter the language names the user can provide you may be vulnerable. The pollution should just be harmless data but this can cause problems for applications not expecting these properties to exist and can result in strange behavior or application crashes, i.e. a potential DOS vector. If your website or application does not render user provided data it should be unaffected. Versions 9.18.2 and 10.1.2 and newer include fixes for this vulnerability. If you are using version 7 or 8 you are encouraged to upgrade to a newer release.

### Impact Affected versions of this package are vulnerable to Prototype Pollution. A malicious HTML code block can be crafted that will result in prototype pollution of the base object's prototype during highlighting. If you allow users to insert custom HTML code blocks into your page/app via parsing Markdown code blocks (or similar) and do not filter the language names the user can provide you may be vulnerable. The pollution should just be harmless data but this can cause problems for applications not expecting these properties to exist and can result in strange behavior or application crashes, i.e. a potential DOS vector. _If your website or application does not render user provided data it should be unaffected._ ### Patches Versions 9.18.2 and 10.1.2 and newer include fixes for this vulnerability. If you are using version 7 or 8 you are encouraged to upgrade to a newer release. ### Workarounds #### Patch your library Manually patch your library to create null objects for both `languages` and `aliases`: ```js const HLJS = function(hljs) { // ... var languages = Object.create(null); var aliases = Object.create(null); ``` #### Filter out bad data from end users: Filter the language names that users are allowed to inject into your HTML to guarantee they are valid. ### References * [What is Prototype Pollution?](https://codeburst.io/what-is-prototype-pollution-49482fc4b638) * https://github.com/highlightjs/highlight.js/pull/2636 ### For more information If you have any questions or comments about this advisory: * Please file an issue against [highlight.js](https://github.com/highlightjs/highlight.js/issues/)

### Impact Affected versions of this package are vulnerable to Prototype Pollution. A malicious HTML code block can be crafted that will result in prototype pollution of the base object's prototype during highlighting. If you allow users to insert custom HTML code blocks into your page/app via parsing Markdown code blocks (or similar) and do not filter the language names the user can provide you may be vulnerable. The pollution should just be harmless data but this can cause problems for applications not expecting these properties to exist and can result in strange behavior or application crashes, i.e. a potential DOS vector. _If your website or application does not render user provided data it should be unaffected._ ### Patches Versions 9.18.2 and 10.1.2 and newer include fixes for this vulnerability. If you are using version 7 or 8 you are encouraged to upgrade to a newer release. ### Workarounds #### Patch your library Manually patch your library to create null objects for both `languages` and `aliases`: ```js const HLJS = function(hljs) { // ... var languages = Object.create(null); var aliases = Object.create(null); ``` #### Filter out bad data from end users: Filter the language names that users are allowed to inject into your HTML to guarantee they are valid. ### References * [What is Prototype Pollution?](https://codeburst.io/what-is-prototype-pollution-49482fc4b638) * https://github.com/highlightjs/highlight.js/pull/2636 ### For more information If you have any questions or comments about this advisory: * Please file an issue against [highlight.js](https://github.com/highlightjs/highlight.js/issues/)

Highlight.js es un resaltador de sintaxis escrito en JavaScript. Highlight.js versiones anteriores a 9.18.2 y 10.1.2 son vulnerables a una Contaminación de Prototipo. Un bloque de código HTML malicioso puede ser diseñado lo que resultará en la contaminación del prototipo del prototipo del objeto base durante el resaltado. Si permite a usuarios insertar bloques de código HTML personalizados en su página y aplicación por medio del análisis de bloques de código Markdown (o similar) y no filtrar los nombres del idioma que el usuario puede proporcionar, puede ser vulnerable. La contaminación debería ser solo datos inofensivos, pero esto puede causar problemas para las aplicaciones que no esperan que se presenten estas propiedades y puede resultar en un comportamiento extraño o fallos de la aplicación, es decir, un vector de DOS potencial. Si su sitio web o aplicación no proporciona los datos proporcionados por el usuario, no debería estar afectado. Versiones 9.18.2 y 10.1. 2 y más recientes incluyen correcciones para esta vulnerabilidad. Si está usando la versión 7 o 8, le recomendamos que actualice a una versión más reciente