Tiptap: Quadratic ReDoS in block and inline Markdown attribute parsing

Summary

## Summary

`@tiptap/core` contains two quadratic regular-expression denial-of-service paths in its default Markdown attribute parsers. Pandoc-style block attributes use two unanchored greedy expressions that rescan repeated `__QUOTED_0` prefixes. Inline shortcode attributes use another unanchored greedy key expression that rescans a long word-character run when no equals sign follows.

The public `createAtomBlockMarkdownSpec` and `createBlockMarkdownSpec` helpers call the vulnerable Pandoc-style parser; `createInlineMarkdownSpec` calls the separately vulnerable shortcode parser. Using unmodified npm 3.29.2, a complete 20,508-byte atom-block token took approximately 1.40 seconds while an equal-length control took 0.29 ms. A complete 32,776-byte inline token took approximately 2.21 seconds while its equal-length control took 0.19 ms. Current repository `main` commit `5158212970344952dd9918b6a44bfb400d7fb6c1` retains both expressions.

## Block attribute root cause

`packages/core/src/utilities/markdown/attributeUtils.ts` uses both `matchAll` and `replace` with `/([a-zA-Z][\w-]*)\s*=\s*(__QUOTED_\d+__)/g`. The candidate is `'__QUOTED_0'.repeat(n) + '__QUOTED_0__'`. There are no quotes, so the preceding replacement leaves it unchanged. At each `Q`, the greedy key-name expression consumes the remaining word-character run, the required equals sign fails, and the unanchored engine restarts at the next `Q`. This yields `O(n^2)` work, and the cleanup pass repeats it.

A complete public-API proof is:

```js import { createAtomBlockMarkdownSpec } from '@tiptap/core' const tokenizer = createAtomBlockMarkdownSpec({ nodeName: 'probe' }).markdownTokenizer const attack = '__QUOTED_0'.repeat(2048) + '__QUOTED_0__' const source = `:::probe {${attack}} :::\n` const started = performance.now() tokenizer.tokenize(source, [], {}) console.log(performance.now() - started) ```

Measured complete-tokenizer timings were 6.23, 23.12, 88.93, 369.10, and 1,400.17 ms at 1,308, 2,588, 5,148, 10,268, and 20,508 bytes. Equal-length controls took 0.07 to 0.29 ms. The directly exported parser took 5,645.71 ms at 40,972 bytes while its control took 0.64 ms.

## Inline attribute root cause

`packages/core/src/utilities/markdown/createInlineMarkdownSpec.ts` uses `/(\w+)=(?:"([^"]*)"|'([^']*)')/g`. For a long word-character run without an equals sign, `\w+` consumes the remaining suffix, `=` fails, and the unanchored engine restarts at the next character. The default inline tokenizer extracts this attacker string directly from a syntactically complete `[shortcode attributes]` token.

```js import { createInlineMarkdownSpec } from '@tiptap/core' const tokenizer = createInlineMarkdownSpec({ nodeName: 'probe', selfClosing: true }).markdownTokenizer const source = `[probe ${'0'.repeat(32768)}]` const started = performance.now() tokenizer.tokenize(source, [], {}) console.log(performance.now() - started) ```

At 1,032, 2,056, 4,104, 8,200, 16,392, and 32,776 bytes, candidates took 3.24, 12.88, 54.82, 136.91, 557.83, and 2,209.47 ms. Equal-length hyphen controls took 0.02 to 0.19 ms.

## Impact

Applications parsing attacker-controlled Markdown with these helpers can have a browser main thread, server event loop, or worker blocked by a small input. Persisted documents can repeatedly freeze clients; repeated requests can exhaust server-side parsing capacity. Editors that only consume validated ProseMirror JSON and never invoke the Markdown parsing path are not directly affected through document content.

## History and remediation

Commit `35645d94ae9cd73448a564104c2e08f64e9564bc` introduced both parsers on 14 October 2025, first released in 3.7.0. Versions 3.7.0 through current 3.29.2 and current `main` remain affected. Official issue, PR, and repository-advisory searches found no duplicate.

Require a start-of-string or whitespace boundary before both key-value parsers, and preferably replace the multi-pass placeholder and shortcode regex designs with deterministic single-pass tokenizers. Keep quoted values out-of-band so attacker input cannot collide with predictable `__QUOTED_n__` placeholders. Add complete block and inline Markdown-tokenizer scaling regressions with equal-length controls.

Please credit GitHub user `joostgrunwald` as finder/reporter.