Tiptap: Quadratic ReDoS in block and inline Markdown attribute parsing

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:

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.

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.