🚨 [security] Update markdown-it 12.3.2 → 14.2.0 (major)

[depfu]

---

🚨 Your current dependencies have known security vulnerabilities 🚨

This dependency update fixes known security vulnerabilities. Please see the details below and assess their impact carefully. We recommend to merge and deploy this as soon as possible!

---

Here is everything you need to know about this upgrade. Please take a good look at what changed and the test results before merging this pull request.

What changed?

✳️ markdown-it (12.3.2 → 14.2.0) · Repo · Changelog

Security Advisories 🚨

🚨 markdown-it: Quadratic complexity DoS in smartquotes rule via replaceAt string operations

Summary

A quadratic time complexity vulnerability exists in markdown-it's smartquotes rule (enabled via the typographer: true option). An attacker can craft a markdown input consisting of consecutive quotation marks that causes the parser to consume excessive CPU time, leading to denial of service.

Details

The vulnerability is in the replaceAt() helper function used by the smartquotes rule in lib/rules_core/smartquotes.mjs:

function replaceAt (str, index, ch) {
  return str.slice(0, index) + ch + str.slice(index + 1)
}

When markdown-it processes a text token containing many quotation marks (either " or ') with typographer: true, the smartquotes rule iterates through each quote character and calls replaceAt() to substitute it with a typographic (curly) quote. Each call to replaceAt() creates three new string slices and concatenates them, which is an O(n) operation where n is the length of the string.

Since this is called once per quote character in the token, and there are n quote characters, the total time complexity becomes O(n^2).

The root cause is that the smartquotes rule modifies token.content in place using string slicing rather than building the result incrementally. The process_inlines() function (line 14) processes each quote in the text token, and for matching quote pairs, calls replaceAt() on both the opening and closing token's content (lines 151-152). When the entire input is a single text token of quote characters, this results in quadratic behavior.

PoC

const md = require('markdown-it');
const instance = md({ typographer: true });
// 160,000 consecutive double-quote characters

const payload = '"'.repeat(160000);
console.time('render');

instance.render(payload);

console.timeEnd('render');

// Output: render: ~21000ms (21 seconds)
// Compare with typographer disabled:

const safe = md({ typographer: false });

console.time('render-safe');

safe.render(payload);

console.timeEnd('render-safe');

// Output: render-safe: ~8ms

Measured timing on a modern system:

• 10,000 quotes: ~19ms
• 20,000 quotes: ~51ms
• 40,000 quotes: ~212ms
• 80,000 quotes: ~5,430ms
• 160,000 quotes: ~21,198ms

The scaling is clearly superlinear (quadratic), with the 80K->160K step showing a ~3.9x increase for a 2x input increase, consistent with O(n^2).

Impact

Applications that render user-supplied markdown with typographer: true are vulnerable to denial of service. An attacker can submit a relatively small payload (160KB of quote characters) that causes the server to spend over 21 seconds processing a single request. Repeated submissions can exhaust server CPU resources and prevent legitimate users from being served.

The impact is mitigated by the fact that the typographer option defaults to false and must be explicitly enabled. However, the typographer feature is commonly enabled in production applications that want smart typography, and the markdown-it documentation prominently suggests enabling it.

A suggested fix would be to replace the replaceAt() approach with an array-based or StringBuilder-style approach that collects all replacements and applies them in a single pass, reducing the time complexity to O(n).

🚨 markdown-it is has a Regular Expression Denial of Service (ReDoS)

Versions of the package markdown-it from 13.0.0 and before 14.1.1 are vulnerable to Regular Expression Denial of Service (ReDoS) due to the use of the regex /*+$/ in the linkify function. An attacker can supply a long sequence of * characters followed by a non-matching character, which triggers excessive backtracking and may lead to a denial-of-service condition.

Release Notes

14.2.0 (from changelog)

Added

• isPunctCharCode to utilities.

Fixed

• Don't end HTML comment blocks on a blank line, #1155.
• Properly recognize astral chars (surrogates) in delimiter scans for emphasis-like markers, #1072. Big thanks to @tats-u for his global efforts with improving CJK support.
• Preserve unicode whitespaces when trimm headings/paragraphs, #1074.
• More strict entities decode to avoid false positives ;, #1096.
• Restore block parser state on fail in lheading rule, #1131.

Security

• Fixed poor smartquotes perfomance on > 70k quotes in single block
• Bumped linkify-it to 5.0.1 with fixed potential perfomance issues.

14.1.1 (from changelog)

Security

• Fixed regression from v13 in linkify inline rule. Specific patterns could cause high CPU use. Thanks to @ltduc147 for report.

14.1.0 (from changelog)

Changed

• Updated CM spec compatibility to 0.31.2, #1009.

Fixed

• Fixed quadratic complexity when parsing references, #996.
• Fixed quadratic output size with pathological user input in tables, #1000.

14.0.0 (from changelog)

Changed

• Drop ancient browsers support (use .fromCodePoint and other features).
• Rewrite to ESM (including all plugins/deps). CJS fallback still available. No signatures changed, except markdown-it-emoji plugin.
• Dropped dist/ folder from repo, build on package publish.
• Set punicode.js as external dependency.

Fixed

• Html tokens inside img alt are now rendered as their original text, #896.
• Hardbreaks inside img alt are now rendered as newlines.

13.0.2 (from changelog)

Security

• Fixed crash/infinite loop caused by linkify inline rule, #957.

Fixed

• Throw an error if 3rd party plugin doesn't increment line or pos counters (previously, markdown-it would likely go into infinite loop instead), #847.

13.0.1 (from changelog)

Fixed

• Bumped linkify-it to 4.0.1. That should fix some hangs, caused by wrong
  data, returned from linkify-it.

13.0.0 (from changelog)

Added

• Added a new token type text_special to store escaped characters, same as text but unaffected by replacement plugins (smartquotes, typographer, linkifier, etc.).
• Added a new rule text_join in core ruler. Text replacement plugins may choose to insert themselves before it.

Changed

• (p) is no longer replaced with § by typographer (conflicts with ℗), #763.
• text_collapse rule is renamed to fragments_join.

Fixed

• Smartquotes, typographic replacements and plain text links can now be escaped with backslash (e.g. \(c) or google\.com are no longer replaced).
• Fixed collision of emphasis and linkifier (so http://example.org/foo._bar_-_baz is now a single link, not emphasized). Emails and fuzzy links are not affected by this.

Does any of this look wrong? Please let us know.

Commits

See the full diff on Github. The new version differs by more commits than we can show here.

↗️ linkify-it (indirect, 3.0.2 → 5.0.1) · Repo · Changelog

Release Notes

5.0.1 (from changelog)

• Fixed DoS in fuzzy links/emails search.
• Reworked search logic - check each pattern separate, use g regexes instead of slice.
• Removed internal cache - useless overcomplication.

5.0.0 (from changelog)

• Rewrite to ESM.

4.0.1 (from changelog)

• Fix http:// incorrectly returned as a link by matchStart.

4.0.0 (from changelog)

• Add matchAtStart method to match full URLs at the start of the string.
• Fixed paired symbols ((), {}, "", etc.) after punctuation.
• --- option now affects parsing of emails (e.g. user@example.com---)

3.0.3 (from changelog)

• Fixed #98. Don't count ; at the end of link (when followed with space).

Does any of this look wrong? Please let us know.

Commits

See the full diff on Github. The new version differs by 36 commits:

• 5.0.1 released
• Add funding field to ackage.json
• Fix fuzzy link/email scan perfomance
• Update .github configs
• 5.0.0 released
• Code cleanup
• orphaned scripts cleanup
• readme: require => import
• eslint: switch to standard base
• lint: fix indent
• lint: remove block padding
• lint: use obj shortland
• lint: remove spaces
• Add cjs build
• Deps bump
• Fix demo & docs build
• nyc => c8
• var => const/let
• lint: remove semi
• CI: bump nodejs version
• rewrite core to ESM
• 4.0.1 released
• Fix matchStart for incomplete links
• 4.0.0 released
• Add recent changes to changelog
• Fix links followed by hyphen
• Fix parenthesis after commas
• Add `matchAtStart` method
• Update funding info
• Update status badge
• CI: Travis => Github Actions
• Add funding info
• Move .eslintignore to main config
• Deps bump
• 3.0.3 released
• Don't count `;` at the end of link (when followed with space)

🆕 punycode.js (added, 2.3.1)

---

Depfu will automatically keep this PR conflict-free, as long as you don't add any commits to this branch yourself. You can also trigger a rebase manually by commenting with @depfu rebase.

All Depfu comment commands

@​depfu rebase

Rebases against your default branch and redoes this update

@​depfu recreate

Recreates this PR, overwriting any edits that you've made to it

@​depfu merge

Merges this PR once your tests are passing and conflicts are resolved

@​depfu cancel merge

Cancels automatic merging of this PR

@​depfu close

Closes this PR and deletes the branch

@​depfu reopen

Restores the branch and reopens this PR (if it's closed)

@​depfu pause

Ignores all future updates for this dependency and closes this PR

@​depfu pause [minor|major]

Ignores all future minor/major updates for this dependency and closes this PR

@​depfu resume

Future versions of this dependency will create PRs again (leaves this PR as is)