Leandro Pereira

**Name of the Vulnerable Software and Affected Versions** mdex versions 0.11.3 through 0.12.2 mdex native versions 0.1.0 through 0.2.2 **Description** Improper neutralization of input during web page generation allows stored or reflected cross-site scripting via attacker-controlled Markdown. When syntax highlighting and full info-string forwarding (`render: [full info string: true]`) are enabled, the Lumis adapter copies the value of a code fence's `highlight lines class` info-string attribute unescaped into the class attribute of every rendered line. The `comrak nif::lumis adapter::LumisAdapter::parse custom attributes()` function shlex-parses the info string and stores key-value pairs verbatim. Subsequently, `highlight lines config` pulls `highlight lines class` into the per-line class value, and `write highlighted()` interpolates that value directly into the class attribute of the per-line `<div>`. A single-quoted shell token can preserve an inner double quote, allowing an attacker to terminate the class attribute and inject arbitrary HTML and JavaScript. This can lead to session theft and account takeover without requiring authentication or special privileges. **Recommendations** Update mdex to version 0.12.3 or later. Update mdex native to version 0.2.3 or later. As a temporary workaround, do not enable full info-string forwarding (`render: [full info string: true]`) when rendering untrusted Markdown. Restrict `highlight lines class` values to a safe character set (e.g., `[A-Za-z0-9 -]`) before rendering.

**Name of the Vulnerable Software and Affected Versions** mdex versions 0.11.0 through 0.12.2 mdex native versions 0.1.0 through 0.2.2 **Description** An unauthenticated attacker can cause a denial of service through unbounded memory allocation. The issue occurs when the `parse highlight lines()` function in the native adapter eagerly expands a user-controlled inclusive line range from a fenced code block's `highlight lines` decorator into a `Vec<usize>` without an upper bound on the range size. An attacker providing Markdown rendered via `MDEx.to html/2` can specify an extremely large range, forcing the system to allocate excessive memory and abort the BEAM, which denies service to all users of the rendering process. Additionally, the per-line write loop performs a linear scan over the vector, resulting in quadratic cost for rendering. Exploitation requires the application to enable code-block decorators by setting both `github pre lang` and `full info string` render options and configuring an inline syntax-highlight formatter. **Recommendations** Update mdex to version 0.12.3 or later. Update mdex native to version 0.2.3 or later. As a temporary workaround, disable code-block decorators by leaving the `github pre lang` and `full info string` render options unset or avoid configuring an inline syntax-highlight formatter to prevent the parsing of `highlight lines` specifications.

**Name of the Vulnerable Software and Affected Versions** leandrocp MDEx versions 0.4.3 through 0.13.1 **Description** An excessive allocation issue exists when the `MDEx.parse document/2` function accepts a `{:json, json}` source. The private `json to node/1` function passes an attacker-controlled `node type` value to `Module.concat/1`, which subsequently calls `String.to atom/1`. This process creates a new atom for every distinct value provided. Because atoms are not garbage collected on the BEAM (the Erlang Virtual Machine), a specially crafted JSON document with unique `node type` values at each deeply nested node can exhaust the default atom table. This leads to an unauthenticated denial-of-service by aborting the entire Erlang VM and terminating all processes on the node. **Recommendations** Update leandrocp MDEx to version 0.13.2 or later. As a temporary workaround, do not pass untrusted or attacker-controlled input to the `{:json, ...}` source of `MDEx.parse document/2`.

**Name of the Vulnerable Software and Affected Versions** mdex versions 0.11.0 through 0.12.2 mdex native versions 0.1.0 through 0.2.2 **Description** A memory leak occurs in the native rendering code when processing documents containing escaped-tag nodes. The conversion of each `%MDEx.EscapedTag{}` node into its native representation via the Rust NIF (Native Implemented Function) uses `Box::leak` on the caller-supplied literal string. This causes the memory allocation to persist for the entire lifetime of the operating system process without being freed. Since the number of nodes and the length of the literals are attacker-controlled and lack size caps or rate limits, repeated rendering of such documents leads to unbounded native memory exhaustion. This can be triggered through the `MDEx.to html/1` endpoint or any API that renders a `%MDEx.Document{}`. Consequently, an attacker can cause a denial of service by exhausting the resident memory of the BEAM process, leading to a system crash. **Recommendations** Update mdex to version 0.12.3 or later. Update mdex native to version 0.2.3 or later.

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**Name of the Vulnerable Software and Affected Versions** leandrocp mdex versions 0.8.3 through 0.13.1 **Description** Improper neutralization of input during web page generation allows cross-site scripting (XSS) via unsanitized URL schemes in Quill Delta output. The function `to delta/2` converts Markdown into a Quill Delta, and the function `default convert node/3` copies URLs from link, wikilink, or image nodes directly into the Delta `link` or `image` attributes without normalization or applying a scheme allowlist. An attacker providing Markdown text can include a `javascript:` URL that is passed verbatim into the Delta attribute. When a downstream renderer converts this Delta to HTML, the attribute becomes an `<a href>` or `<img src>`, executing the script in the browser of the user. Links and wikilinks are the primary vectors as they execute on click, while images have lower impact in modern browsers. **Recommendations** Update leandrocp mdex to version 0.13.2 or later. As a temporary workaround, sanitize the Quill Delta produced by `to delta/2` before rendering by dropping or blanking any `link` or `image` value with a URL scheme not included in a safe allowlist (e.g., http, https, mailto, tel).