chore(deps): update dependency js-yaml@4 to v5 [security] - autoclosed

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
js-yaml@4	^4.3.1 → ^5.4.2

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js-yaml: maxTotalMergeKeys does not limit CPU use for empty merge sources

CVE-2026-84375 / GHSA-2883-xcg3-v3hh

More information

Details

Summary

maxTotalMergeKeys does not count empty mappings. An attacker can repeatedly merge a large sequence of them and consume significant CPU without reaching the configured limit.

Example

arr: &arr [{}, {}, {}, ...] # N empty mappings
targets:
  - <<: *arr                # repeated K times

For every target, the loader iterates all N elements of arr. This results in O(N * K) work while totalMergeKeys remains unchanged.

PoC

import { performance } from 'node:perf_hooks'
import { load, YAML11_SCHEMA } from 'js-yaml'

const n = 20000

const src =
  'arr: &arr [' + '{},'.repeat(n).slice(0, -1) + ']\n' +
  'targets:\n' +
  '  - <<: *arr\n'.repeat(n)

const started = performance.now()

load(src, { schema: YAML11_SCHEMA })

console.log(`${(performance.now() - started).toFixed(1)} ms`)

Observed results:

N	YAML size	Time
800	~13 KB	~20 ms
3200	~50 KB	~180 ms
20000	~500 KB	~13 s

Impact

An attacker can submit a relatively small YAML document that causes prolonged CPU consumption despite the default maxTotalMergeKeys limit.

Fix

Count each merge-source mapping as one budget unit, in addition to counting its keys.

Difference with v5

In v3 & v4, merge is enabled by default. So, the severity score is higher.

Severity

• CVSS Score: 7.5 / 10 (High)
• Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

• https://github.com/nodeca/js-yaml/security/advisories/GHSA-2883-xcg3-v3hh
• https://nvd.nist.gov/vuln/detail/CVE-2026-84375
• https://github.com/nodeca/js-yaml/pull/797
• https://github.com/nodeca/js-yaml/commit/3485bc06ff8a0251505f44a00414d90df2466639
• https://github.com/nodeca/js-yaml/commit/6a8e05f9a485188ed730ac81e81ae221352ef480
• https://github.com/nodeca/js-yaml/commit/d90b6612a5a84385bdcb556c44578eac76dc0f6b
• https://github.com/nodeca/js-yaml/releases/tag/3.15.2
• https://github.com/nodeca/js-yaml/releases/tag/4.3.2
• https://github.com/advisories/GHSA-2883-xcg3-v3hh

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

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Release Notes

nodeca/js-yaml (js-yaml@4)

v5.4.2

Compare Source

Fixed

• forceQuotes no longer quotes non-string scalars, #​798.

v5.4.1

Compare Source

v5.4.0

Compare Source

Added

• Added the scalarStyleRules dumper option to customize string formatting.
  See Scalar styling for details.

Changed

• [breaking] Flattened the low-level AST node style representation. Scalar
  and collection nodes now use SCALAR_STYLE and COLLECTION_STYLE values;
  explicit tags use the separate tagged property. Alias nodes now contain
  only kind and anchor. This only affects code that directly constructs or
  edits AST nodes.
• [breaking] The sortKeys option was rewritten using AST mutation to avoid
  side effects.
• Reworked scalar style selection. This can change formatting without changing
  loaded values; in particular, whitespace-only strings are now double-quoted.

Fixed

• Accept a byte order mark at the start of each document in a stream, #​791.
• Produce valid flow mappings with quoteFlowKeys and flowSkipColonSpace,
  including alias and property-only keys, #​786.
• Preserve empty scalar items when converting block sequences to flow style.
• Do not apply the 1024-character simple-key limit to flow mapping keys.
• Count Unicode code points, rather than UTF-16 code units, for the
  1024-character simple-key limit.
• Add an explicit document-end marker after keep-chomped block scalars when
  needed to preserve trailing newlines.

v5.3.0

Compare Source

This release focuses on reworking the documentation and making small
architectural improvements before moving forward.

Added

• Added completely new documentation.
• Exported DUMP_SCHEMA, the default schema used by the dumper.
• Added YAMLException.throwAt() for throwing an error at a source position.

Changed

• Changed flat constant exports to grouped exports: EVENT_ID, SCALAR_STYLE,
  COLLECTION_STYLE, and CHOMPING_MODE, along with their value types. The old
  exports are still preserved, but deprecated.
• Made identify mandatory for custom tag definitions. Use
  identify: () => false for load-only tags.

Deprecated

• Deprecated flat constant exports. Use grouped ones instead.

Removed

• Removed the MERGE_KEY export (not used anymore after last fixes).

Fixed

• Validate << sequence items at merge time, so aliased merge sources are
  checked too.
• Resolve << outside of a mapping key as the plain string '<<', matching
  v4, instead of leaking an internal symbol into the result.

v5.2.3

Compare Source

Fixed

• Prevent prototype fallback when resolving tags and mapping entries, #​782.
• Resolve !!timestamp years 0000-0099 correctly, #​775.
• Preserve implicit null mapping values before document markers and reject
  unpaired mapping event streams, #​784.
• Preserve folded scalar values with tab-indented lines when round-tripping a
  parsed AST through present(); dump() and loading are unaffected, #​780.

v5.2.2

Compare Source

Fixed

• Quote flow scalars where a colon precedes a flow indicator, #​773.

Security

• Avoid exponential parsing time for nested flow sequence pairs.

v5.2.1

Compare Source

Fixed

• Add Map support to !!omap (should work when realMapTag used)

Security

• Remove quadratic complexity from !!omap addItem. Regression from v5
  (usually not critical, because YAML11_SCHEMA is not default anymore).

v5.2.0

Compare Source

Added

• Added maxTotalMergeKeys (10000) loader option to limit the total number of
  keys processed by YAML merge (<<) across one load() / loadAll() call.
• Added maxAliases (-1) loader option to limit the number of YAML aliases per
  document.

Removed

• maxMergeSeqLength replaced with maxTotalMergeKeys for limiting YAML merge
  processing.

Fixed

• Round-trip of integers with exponential form (>= 1e21)

v5.1.0

Compare Source

Added

• Collection tags can finalize an incrementally populated carrier into a
  different result value.

Changed

• [breaking] quoteStyle now selects the preferred quote style; use the
  restored forceQuotes option to force quoting non-key strings.

v5.0.0

Compare Source

Added

• Added named exports for schemas, tags, parser events and AST utilities.
• Reworked JSON_SCHEMA and CORE_SCHEMA with spec-compliant scalar resolution
  rules, and added YAML11_SCHEMA.
• Added realMapTag for lossless mappings with non-string and complex keys.
  Object-based mappings now reject complex keys instead of stringifying them.
• Added dump() transform option for changing the generated AST before
  rendering.
• Added dump() options seqInlineFirst, flowBracketPadding,
  flowSkipCommaSpace, flowSkipColonSpace, quoteFlowKeys, quoteStyle and
  tagBeforeAnchor.
• Added formal data layers (events and AST) for modular data pipelines.
  • Added low-level parser (to events), presenter and visitor APIs.
• Added the YAML Test Suite to the
  test set.

Changed

• See the migration guide for upgrade notes.
• Rewritten in TypeScript and reorganized the public API around flat named
  exports.
• Reduced the set of exported schemas:
  • YAML 1.2 schemas: CORE_SCHEMA (loader default), JSON_SCHEMA,
    FAILSAFE_SCHEMA.
  • YAML11_SCHEMA, a combination of all YAML 1.1 tags (YAML 1.1 does not
    specify a schema, only "types").
• load/dump default behaviour is now specified exactly via schemas:
  • load uses CORE_SCHEMA, without !!merge by default.
  • dump uses YAML11_SCHEMA + CORE_SCHEMA for the quoting check, to
    guarantee backward compatibility by default.
• !!set is now loaded as a JavaScript Set.
• Replaced the Type API with a tags API. Similar, but more precise and
  simpler. See examples for details. Tags can be defined via
  defineScalarTag(), defineSequenceTag() and defineMappingTag(), or as a
  spread + override of an existing tag.
• Renamed Schema.extend() to Schema.withTags().
• Expanded YAML 1.2 conformance and improved handling of directives, document
  markers, block keys, multiline scalars, tag syntax and other things.
• load() now throws on empty input instead of returning undefined.
• Moved browser builds to the js-yaml/browser export.
• Deprecated the loadAll signature with an iterator (still works, but is a
  candidate for removal).

Removed

• Removed deprecated safeLoad(), safeLoadAll() and safeDump() exports.
• Removed DEFAULT_SCHEMA and the nested types export.
• Removed loader options onWarning, legacy and listener.
• Removed dumper options styles, replacer, noCompatMode, condenseFlow,
  quotingType and forceQuotes. Renamed noArrayIndent to seqNoIndent.
  Formatting and representation are now configured through presenter options,
  schemas and tag definitions. See migration guide on how to replace.
• Removed support for importing internal files from lib/.

v4.3.2

Compare Source

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Incompatible js-yaml major override

High Severity

The js-yaml@4 override now resolves to ^5.4.2, a major that drops the default export and changes load() (empty input throws; default schema is YAML 1.2 CORE_SCHEMA without merge). Transitive v4 consumers @changesets/parse and cosmiconfig still call the v4 API, so changeset parsing and YAML config loading can fail at runtime.

 

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