esm: avoid super-linear data URL MIME regex by skdas20 · Pull Request #61951 · nodejs/node

skdas20 · 2026-02-23T08:41:25Z

Fixes: #61904

This updates ESM data URL MIME extraction regexes to remove overlapping quantifiers that allow super-linear backtracking.

Replaced (?:[^,]*?)(;base64)?, with (?:;[^,]*)?, in:
- lib/internal/modules/esm/get_format.js
- lib/internal/modules/esm/load.js

Behavior is preserved for existing valid/invalid data: URL shapes while avoiding pathological backtracking on crafted inputs.

nodejs-github-bot · 2026-02-23T08:41:31Z

Review requested:

@nodejs/loaders

jsumners-nr

Where are tests to assert the undesired behavior is resolved by the changes?

skdas20 · 2026-02-23T15:10:46Z

Added regression coverage in test/parallel/test-esm-data-url-format-regex-backtracking.js (commit 740d1320).

The test exercises defaultGetFormat() with a long malformed data: URL (data:a/aaaa...B) that used to trigger super-linear backtracking, and asserts the path now completes within a platform-adjusted bound.

aduh95 · 2026-02-24T14:34:36Z

+// Flags: --expose-internals
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const { defaultGetFormat } = require('internal/modules/esm/get_format');
+
+// Regression test for #61904. This malformed data URL path is crafted to
+// stress the MIME regex without triggering URL parsing failures.
+const longPath = `data:a/${'a'.repeat(2 ** 17)}B`;
+const start = process.hrtime.bigint();
+const format = defaultGetFormat(new URL(longPath), { parentURL: undefined });
+const elapsedMs = Number(process.hrtime.bigint() - start) / 1e6;
+
+assert.strictEqual(format, null);
+assert.ok(
+  elapsedMs < common.platformTimeout(1000),
+  `Expected format detection to complete quickly, took ${elapsedMs}ms`,
+);


This is going to be inherently flaky, could we instead write a benchmark?

skdas20 · 2026-02-26T18:50:18Z

CI has not started yet on this PR (currently no check runs, and needs-ci is present).

Could a collaborator please add the request-ci label to trigger Jenkins?

JakobJingleheimer · 2026-02-26T19:12:57Z

There are no official approvals on this PR, so CI cannot be started (it will refuse).

skdas20 · 2026-07-25T19:31:03Z

Replaced the timing-based regression test with a benchmark (esm/get-data-protocol-format) parameterized over path length, per @aduh95's suggestion — a backtracking regression will now show up as an ops/sec cliff instead of relying on wall-clock assertions in CI.

Could a collaborator add request-ci to kick off Jenkins?

nodejs-github-bot · 2026-07-25T19:57:24Z

CI: https://ci.nodejs.org/job/node-test-pull-request/75139/

skdas20 · 2026-07-29T14:17:17Z

Squashed into a single signed commit and force-pushed — the diff is unchanged (regex fix in get_format.js/load.js plus the esm/get-data-protocol-format benchmark).

Doing this pre-emptively since @trivikr flagged the same missing Signed-off-by on #62010 and #62009, and this one is already approved — should be one less thing blocking the commit queue.

mcollina · 2026-07-29T14:55:54Z

check the commit lint

codecov · 2026-07-29T16:20:23Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.14%. Comparing base (da5efc4) to head (cf0eb3b).
⚠️ Report is 1468 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61951      +/-   ##
==========================================
+ Coverage   88.84%   90.14%   +1.30%     
==========================================
  Files         674      746      +72     
  Lines      204957   242818   +37861     
  Branches    39309    45766    +6457     
==========================================
+ Hits       182087   218891   +36804     
- Misses      15088    15420     +332     
- Partials     7782     8507     +725

Files with missing lines	Coverage Δ
lib/internal/modules/esm/get_format.js	`95.20% <100.00%> (+1.10%)`	⬆️
lib/internal/modules/esm/load.js	`91.40% <100.00%> (-0.08%)`	⬇️

... and 520 files with indirect coverage changes

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The MIME regex used for data: URLs could backtrack super-linearly on a malformed URL lacking a ',' separator. Make the optional parameter group anchored on ';' so it cannot overlap with the media-type group. Adds a benchmark (esm/get-data-protocol-format) parameterized over path length, so a backtracking regression shows up as an ops/sec cliff instead of a wall-clock assertion in a test, per review. Fixes: nodejs#61904 Signed-off-by: skdas20 <skdas5405@gmail.com>

skdas20 · 2026-07-29T16:26:00Z

Thanks @mcollina — line-length was failing: one body line was 74 columns. Rewrapped the message so every line is within 72; the diff is unchanged.

skdas20 · 2026-08-01T06:27:42Z

Status summary for whoever picks this up: the PR is approved, and the lint-commit-message failure @mcollina flagged is fixed (one body line was 74 columns; rewrapped to 72). The force-push that fixed it was message-only — the tree is identical to the one that passed CI on 25 July (https://ci.nodejs.org/job/node-test-pull-request/75139/).

Could a collaborator add request-ci so Jenkins can re-run against the current commit? That looks like the only thing left before this can be queued.

nodejs-github-bot added esm Issues and PRs related to the ECMAScript Modules implementation. needs-ci PRs that need a full CI run. labels Feb 23, 2026

jsumners-nr reviewed Feb 23, 2026

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jsumners-nr approved these changes Feb 24, 2026

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aduh95 reviewed Feb 24, 2026

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avivkeller approved these changes Jul 25, 2026

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avivkeller added the request-ci Add this label to start a Jenkins CI on a PR. label Jul 25, 2026

github-actions Bot removed the request-ci Add this label to start a Jenkins CI on a PR. label Jul 25, 2026

skdas20 force-pushed the fix-61904-data-url-regex-backtracking branch from bd04ddd to 3487338 Compare July 29, 2026 14:17

skdas20 force-pushed the fix-61904-data-url-regex-backtracking branch from 3487338 to cf0eb3b Compare July 29, 2026 16:26

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