Affected: Homebrew: adr-viewer

## Summary

**Type:** Predictable identifier generation. The `toc` plugin and `TableOfContents` directive both default to generating heading IDs of the form `toc_1`, `toc_2`, `toc_3`, ... with no input-derived component. An attacker who can place a heading anywhere in the document can predict which `toc_N` ID it will receive, and can inject HTML elsewhere (in a non-heading context) that uses the same `id="toc_N"` to either (a) shadow the legitimate heading anchor, breaking same-page navigation, or (b) collide with CSS or JavaScript that targets `#toc_N` selectors, redirecting click handlers and styling to attacker-chosen content. **File:** `src/mistune/toc.py` line 36-37 (`heading_id = lambda token, index: "toc_" + str(index + 1)`); `src/mistune/directives/toc.py` line 33 (same default). **Root cause:** the default `heading_id` callback ignores the heading's text content and uses only the headings's order in the document. Two documents rendered together (or one document with attacker-influenced headings spliced into trusted content) produce overlapping `toc_N` IDs. Because `id` attribute uniqueness is required by HTML, browsers behaviour on duplicate IDs is undefined; `document.getElementById('toc_1')` returns the first match, `getElementsByTagName + querySelector` semantics differ across paths, and CSS rules targeting `#toc_1` apply to whichever element matches first in tree order.

## Affected Code

**File:** `src/mistune/toc.py`, lines 33-39.

```python def add_toc_hook(m…

Affected: lepture mistune

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the toc plugin and TableOfContents directive generate heading IDs as predictable toc_N values without slugifying the heading text, allowing attacker-controlled id="toc_N" content to collide with generated anchors and redirect same-page navigation, CSS selectors, or JavaScript handlers. This issue is fixed in version 3.3.0.

Affected: PyPI: mistune

## Summary

**Type:** Predictable identifier generation. The `toc` plugin and `TableOfContents` directive both default to generating heading IDs of the form `toc_1`, `toc_2`, `toc_3`, ... with no input-derived component. An attacker who can place a heading anywhere in the document can predict which `toc_N` ID it will receive, and can inject HTML elsewhere (in a non-heading context) that uses the same `id="toc_N"` to either (a) shadow the legitimate heading anchor, breaking same-page navigation, or (b) collide with CSS or JavaScript that targets `#toc_N` selectors, redirecting click handlers and styling to attacker-chosen content. **File:** `src/mistune/toc.py` line 36-37 (`heading_id = lambda token, index: "toc_" + str(index + 1)`); `src/mistune/directives/toc.py` line 33 (same default). **Root cause:** the default `heading_id` callback ignores the heading's text content and uses only the headings's order in the document. Two documents rendered together (or one document with attacker-influenced headings spliced into trusted content) produce overlapping `toc_N` IDs. Because `id` attribute uniqueness is required by HTML, browsers behaviour on duplicate IDs is undefined; `document.getElementById('toc_1')` returns the first match, `getElementsByTagName + querySelector` semantics differ across paths, and CSS rules targeting `#toc_1` apply to whichever element matches first in tree order.

## Affected Code

**File:** `src/mistune/toc.py`, lines 33-39.

```python def add_toc_hook(m…