CVE-2026-76098

## Summary Mistune v3.3.2 is vulnerable to a Denial of Service (DoS) attack via uncontrolled recursion in the HTML rendering of deeply-nested emphasis tokens. By submitting Markdown containing approximately 1,000 consecutive asterisk characters, an attacker causes the Python process to crash with RecursionError. ## Details The InlineParser's _process_emphasis_delimiters() creates deeply nested <strong> tokens from consecutive emphasis markers (every 2 asterisks add one nesting level). With 1,000 consecutive asterisks, approximately 500 levels of nesting are produced. The HTMLRenderer.render_token() method (src/mistune/renderers/html.py:40-57) renders these tokens recursively: when a token has children, line 48 calls self.render_tokens(token['children'], state), entering child rendering. Each nesting level produces ~2 stack frames, so 500 levels ≈ 1,000 frames, exceeding Python's default recursion limit (sys.getrecursionlimit() = 1000). The emphasis() and strong() methods (lines 80-84) wrap recursively rendered child content in <em> and <strong> tags, perpetuating the recursion. This vulnerability affects all mistune APIs including markdown() and html(). Core vulnerable code path: ```python # src/mistune/renderers/html.py:40-57 def render_token(self, token: Dict[str, Any], state: BlockState) -> str: func = self._get_method(token["type"]) attrs = token.get("attrs") if "raw" in token: text = token["raw"] elif "children" in token: text = self.render_tokens(token["children"], state) else: if attrs: return func(**attrs) else: return func() if attrs: return func(text, **attrs) else: return func(text) ``` The recursive call to render_tokens() on line 48 processes nested child tokens. With 500 levels of nested emphasis/strong tokens, this recursion exceeds Python's default recursion limit of 1000, causing a RecursionError. ```python # src/mistune/renderers/html.py:80-84 d