CVE-2026-110910 (GCVE-0-2026-110910)
Vulnerability from cvelistv5
Published
2026-10-27 06:42
Modified
2026-10-27 19:32
Severity ?
3.7 (Low) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
6.3 (Medium) - CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
CWE
  • CWE-116 - Improper Encoding or Escaping of Output
Summary
### Summary `qs.stringify` with `allowEmptyArrays: true` writes the key of an empty array without encoding it, even though keys are encoded by default. A key that contains `&` (or the configured `delimiter`), `=`, or `#` therefore becomes query string syntax instead of data, so a caller-supplied key name can add parameters to the serialized query string, or cut it short. ### Details In `lib/stringify.js`, the `allowEmptyArrays` branch returns `adjustedPrefix + '[]'` early, before the code that passes every other key through `encoder` and `formatter`. So `{ "x&k=v": ["1"] }` serializes as `x%26k%3Dv%5B0%5D=1`, but `{ "x&k=v": [] }` serializes as `x&k=v[]`. The early return applies at any depth (`{ "a": { "b&k=v": [] } }` gives `a[b&k=v][]`), under every `arrayFormat`, with `allowDots`, and with a custom `encoder`, which is never called for that key. With `encode: false` or `encodeValuesOnly: true`, keys are intentionally left unencoded on every path; those configurations are not affected. #### PoC ```js var qs = require("qs"); var query = qs.stringify({ q: "hi", "x&apiKey=evil&y": [] }, { allowEmptyArrays: true }); // "q=hi&x&apiKey=evil&y[]" qs.parse(query); // { q: "hi", x: "", apiKey: "evil", y: [""] } qs.stringify({ "x#": [], z: "1" }, { allowEmptyArrays: true }); // "x#[]&z=1": in a URL, everything after "#" becomes the fragment ``` #### Fix Applied in 234d505 on `main` and released as v6.17.0, and backported to v6.16.2, v6.15.4, v6.14.3, v6.13.4, and v6.12.6: the key of an empty array goes through `encoder` and `formatter` exactly as the key of any other value does, so `{ "x&apiKey=evil&y": [] }` now serializes as `x%26apiKey%3Devil%26y[]`. Keys that need no encoding serialize as before, with two exceptions that match every other path: the brackets of a nested key are now encoded (`a[b][]` becomes `a%5Bb%5D[]`, which `qs.parse` reads identically), and with `encodeDotInKeys`, a dot in the key becomes `%252E` instead of `%2E` (which `decodeDotInKeys` previously misread as nesting). ### Affected versions - `>=6.12.0 <6.12.6`, fixed in v6.12.6 - `>=6.13.0 <6.13.4`, fixed in v6.13.4 - `>=6.14.0 <6.14.3`, fixed in v6.14.3 - `>=6.15.0 <6.15.4`, fixed in v6.15.4 - `>=6.16.0 <6.16.2`, fixed in v6.16.2 v6.17.0 and later are not affected. `allowEmptyArrays` was introduced in f22b2bc and first shipped in v6.12.0, with this early return. Earlier versions have no `allowEmptyArrays` option and are not affected. ### Impact An application that passes an object whose key names come from untrusted input to `qs.stringify` with `allowEmptyArrays: true` (for example, to forward a parsed JSON body or user-selected fields to an upstream service) can have parameters injected into the resulting query string. The injected parameters are not keys of the object, so deleting or overwriting a key on the object (such as setting a trusted `apiKey` after copying the user's fields) does not remove them; whether the attacker's value or the application's wins depends on how the receiving side handles a duplicate parameter. A `#` in such a key ends the query string early when the result is placed in a URL. `allowEmptyArrays` is off by default, and only keys whose value (after any `filter`) is an empty array are affected.
References
Impacted products
Vendor Product Version
ljharb qs Version: 6.12.0   ≤
Version: 6.13.0   ≤
Version: 6.14.0   ≤
Version: 6.15.0   ≤
Version: 6.16.0   ≤
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "collectionURL": "https://npmjs.com/qs",
          "defaultStatus": "unaffected",
          "packageName": "qs",
          "product": "qs",
          "repo": "https://github.com/ljharb/qs",
          "vendor": "ljharb",
          "versions": [
            {
              "lessThan": "6.12.6",
              "status": "affected",
              "version": "6.12.0",
              "versionType": "semver"
            },
            {
              "lessThan": "6.13.4",
              "status": "affected",
              "version": "6.13.0",
              "versionType": "semver"
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              "lessThan": "6.14.3",
              "status": "affected",
              "version": "6.14.0",
              "versionType": "semver"
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            {
              "lessThan": "6.15.4",
              "status": "affected",
              "version": "6.15.0",
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              "version": "6.16.0",
              "versionType": "semver"
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      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "DucMinhNe"
        },
        {
          "lang": "en",
          "type": "remediation developer",
          "value": "DucMinhNe"
        },
        {
          "lang": "en",
          "type": "remediation reviewer",
          "value": "ljharb"
        }
      ],
      "descriptions": [
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              "value": "\u003cp\u003e### Summary\u003c/p\u003e\u003cp\u003e`qs.stringify` with `allowEmptyArrays: true` writes the key of an empty array without encoding it, even though keys are encoded by default. A key that contains `\u0026amp;` (or the configured `delimiter`), `=`, or `#` therefore becomes query string syntax instead of data, so a caller-supplied key name can add parameters to the serialized query string, or cut it short.\u003c/p\u003e\u003cp\u003e### Details\u003c/p\u003e\u003cp\u003eIn `lib/stringify.js`, the `allowEmptyArrays` branch returns `adjustedPrefix + \u0027[]\u0027` early, before the code that passes every other key through `encoder` and `formatter`. So `{ \"x\u0026amp;k=v\": [\"1\"] }` serializes as `x%26k%3Dv%5B0%5D=1`, but `{ \"x\u0026amp;k=v\": [] }` serializes as `x\u0026amp;k=v[]`. The early return applies at any depth (`{ \"a\": { \"b\u0026amp;k=v\": [] } }` gives `a[b\u0026amp;k=v][]`), under every `arrayFormat`, with `allowDots`, and with a custom `encoder`, which is never called for that key. With `encode: false` or `encodeValuesOnly: true`, keys are intentionally left unencoded on every path; those configurations are not affected.\u003c/p\u003e\u003cp\u003e#### PoC\u003c/p\u003e\u003cp\u003e```js\u003c/p\u003e\u003cp\u003evar qs = require(\"qs\");\u003c/p\u003e\u003cp\u003evar query = qs.stringify({ q: \"hi\", \"x\u0026amp;apiKey=evil\u0026amp;y\": [] }, { allowEmptyArrays: true });\u003c/p\u003e\u003cp\u003e// \"q=hi\u0026amp;x\u0026amp;apiKey=evil\u0026amp;y[]\"\u003c/p\u003e\u003cp\u003eqs.parse(query);\u003c/p\u003e\u003cp\u003e// { q: \"hi\", x: \"\", apiKey: \"evil\", y: [\"\"] }\u003c/p\u003e\u003cp\u003eqs.stringify({ \"x#\": [], z: \"1\" }, { allowEmptyArrays: true });\u003c/p\u003e\u003cp\u003e// \"x#[]\u0026amp;z=1\": in a URL, everything after \"#\" becomes the fragment\u003c/p\u003e\u003cp\u003e```\u003c/p\u003e\u003cp\u003e#### Fix\u003c/p\u003e\u003cp\u003eApplied in 234d505 on `main` and released as v6.17.0, and backported to v6.16.2, v6.15.4, v6.14.3, v6.13.4, and v6.12.6: the key of an empty array goes through `encoder` and `formatter` exactly as the key of any other value does, so `{ \"x\u0026amp;apiKey=evil\u0026amp;y\": [] }` now serializes as `x%26apiKey%3Devil%26y[]`. Keys that need no encoding serialize as before, with two exceptions that match every other path: the brackets of a nested key are now encoded (`a[b][]` becomes `a%5Bb%5D[]`, which `qs.parse` reads identically), and with `encodeDotInKeys`, a dot in the key becomes `%252E` instead of `%2E` (which `decodeDotInKeys` previously misread as nesting).\u003c/p\u003e\u003cp\u003e### Affected versions\u003c/p\u003e\u003cp\u003e- `\u0026gt;=6.12.0 \u0026lt;6.12.6`, fixed in v6.12.6\u003c/p\u003e\u003cp\u003e- `\u0026gt;=6.13.0 \u0026lt;6.13.4`, fixed in v6.13.4\u003c/p\u003e\u003cp\u003e- `\u0026gt;=6.14.0 \u0026lt;6.14.3`, fixed in v6.14.3\u003c/p\u003e\u003cp\u003e- `\u0026gt;=6.15.0 \u0026lt;6.15.4`, fixed in v6.15.4\u003c/p\u003e\u003cp\u003e- `\u0026gt;=6.16.0 \u0026lt;6.16.2`, fixed in v6.16.2\u003c/p\u003e\u003cp\u003ev6.17.0 and later are not affected.\u003c/p\u003e\u003cp\u003e`allowEmptyArrays` was introduced in f22b2bc and first shipped in v6.12.0, with this early return. Earlier versions have no `allowEmptyArrays` option and are not affected.\u003c/p\u003e\u003cp\u003e### Impact\u003c/p\u003e\u003cp\u003eAn application that passes an object whose key names come from untrusted input to `qs.stringify` with `allowEmptyArrays: true` (for example, to forward a parsed JSON body or user-selected fields to an upstream service) can have parameters injected into the resulting query string. The injected parameters are not keys of the object, so deleting or overwriting a key on the object (such as setting a trusted `apiKey` after copying the user\u0027s fields) does not remove them; whether the attacker\u0027s value or the application\u0027s wins depends on how the receiving side handles a duplicate parameter. A `#` in such a key ends the query string early when the result is placed in a URL. `allowEmptyArrays` is off by default, and only keys whose value (after any `filter`) is an empty array are affected.\u003c/p\u003e"
            }
          ],
          "value": "### Summary\n\n\n\n`qs.stringify` with `allowEmptyArrays: true` writes the key of an empty array without encoding it, even though keys are encoded by default. A key that contains `\u0026` (or the configured `delimiter`), `=`, or `#` therefore becomes query string syntax instead of data, so a caller-supplied key name can add parameters to the serialized query string, or cut it short.\n\n\n\n### Details\n\n\n\nIn `lib/stringify.js`, the `allowEmptyArrays` branch returns `adjustedPrefix + \u0027[]\u0027` early, before the code that passes every other key through `encoder` and `formatter`. So `{ \"x\u0026k=v\": [\"1\"] }` serializes as `x%26k%3Dv%5B0%5D=1`, but `{ \"x\u0026k=v\": [] }` serializes as `x\u0026k=v[]`. The early return applies at any depth (`{ \"a\": { \"b\u0026k=v\": [] } }` gives `a[b\u0026k=v][]`), under every `arrayFormat`, with `allowDots`, and with a custom `encoder`, which is never called for that key. With `encode: false` or `encodeValuesOnly: true`, keys are intentionally left unencoded on every path; those configurations are not affected.\n\n\n\n#### PoC\n\n\n\n```js\n\n\n\nvar qs = require(\"qs\");\n\n\n\nvar query = qs.stringify({ q: \"hi\", \"x\u0026apiKey=evil\u0026y\": [] }, { allowEmptyArrays: true });\n\n\n\n// \"q=hi\u0026x\u0026apiKey=evil\u0026y[]\"\n\n\n\nqs.parse(query);\n\n\n\n// { q: \"hi\", x: \"\", apiKey: \"evil\", y: [\"\"] }\n\n\n\nqs.stringify({ \"x#\": [], z: \"1\" }, { allowEmptyArrays: true });\n\n\n\n// \"x#[]\u0026z=1\": in a URL, everything after \"#\" becomes the fragment\n\n\n\n```\n\n\n\n#### Fix\n\n\n\nApplied in 234d505 on `main` and released as v6.17.0, and backported to v6.16.2, v6.15.4, v6.14.3, v6.13.4, and v6.12.6: the key of an empty array goes through `encoder` and `formatter` exactly as the key of any other value does, so `{ \"x\u0026apiKey=evil\u0026y\": [] }` now serializes as `x%26apiKey%3Devil%26y[]`. Keys that need no encoding serialize as before, with two exceptions that match every other path: the brackets of a nested key are now encoded (`a[b][]` becomes `a%5Bb%5D[]`, which `qs.parse` reads identically), and with `encodeDotInKeys`, a dot in the key becomes `%252E` instead of `%2E` (which `decodeDotInKeys` previously misread as nesting).\n\n\n\n### Affected versions\n\n\n\n- `\u003e=6.12.0 \u003c6.12.6`, fixed in v6.12.6\n\n\n\n- `\u003e=6.13.0 \u003c6.13.4`, fixed in v6.13.4\n\n\n\n- `\u003e=6.14.0 \u003c6.14.3`, fixed in v6.14.3\n\n\n\n- `\u003e=6.15.0 \u003c6.15.4`, fixed in v6.15.4\n\n\n\n- `\u003e=6.16.0 \u003c6.16.2`, fixed in v6.16.2\n\n\n\nv6.17.0 and later are not affected.\n\n\n\n`allowEmptyArrays` was introduced in f22b2bc and first shipped in v6.12.0, with this early return. Earlier versions have no `allowEmptyArrays` option and are not affected.\n\n\n\n### Impact\n\n\n\nAn application that passes an object whose key names come from untrusted input to `qs.stringify` with `allowEmptyArrays: true` (for example, to forward a parsed JSON body or user-selected fields to an upstream service) can have parameters injected into the resulting query string. The injected parameters are not keys of the object, so deleting or overwriting a key on the object (such as setting a trusted `apiKey` after copying the user\u0027s fields) does not remove them; whether the attacker\u0027s value or the application\u0027s wins depends on how the receiving side handles a duplicate parameter. A `#` in such a key ends the query string early when the result is placed in a URL. `allowEmptyArrays` is off by default, and only keys whose value (after any `filter`) is an empty array are affected."
        }
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            "Recovery": "NOT_DEFINED",
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            "attackVector": "NETWORK",
            "baseScore": 6.3,
            "baseSeverity": "MEDIUM",
            "exploitMaturity": "NOT_DEFINED",
            "privilegesRequired": "NONE",
            "providerUrgency": "NOT_DEFINED",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "valueDensity": "NOT_DEFINED",
            "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N",
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            "vulnerabilityResponseEffort": "NOT_DEFINED"
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              "cweId": "CWE-116",
              "description": "CWE-116 Improper Encoding or Escaping of Output",
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              "type": "CWE"
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      "providerMetadata": {
        "dateUpdated": "2026-10-27T19:32:36.456Z",
        "orgId": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
        "shortName": "harborist"
      },
      "references": [
        {
          "tags": [
            "vendor-advisory"
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          "url": "https://github.com/ljharb/qs/security/advisories/GHSA-w4cr-vjpx-p82q"
        },
        {
          "tags": [
            "patch"
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          "url": "https://github.com/ljharb/qs/commit/234d5051f5071efaa025a7ca9e4d34a56a460a1b"
        },
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          "tags": [
            "patch"
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        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/ljharb/qs/commit/ad445aa23e4c3a97394c3b9a5f9d7a7159eb1f17"
        },
        {
          "tags": [
            "patch"
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          "url": "https://github.com/ljharb/qs/commit/5d3b1b9ec6afd0cfc760c8e12862873789a32fc8"
        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/ljharb/qs/pull/561"
        },
        {
          "tags": [
            "issue-tracking"
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          "url": "https://github.com/ljharb/qs/issues/626"
        }
      ],
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              "value": "\u003cp\u003eUpgrade to qs 6.17.0 or later, or, on an older release line, to 6.12.6, 6.13.4, 6.14.3, 6.15.4, or 6.16.2.\u003c/p\u003e"
            }
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        }
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      "source": {
        "discovery": "EXTERNAL"
      },
      "title": "qs.stringify with allowEmptyArrays does not encode the keys of empty arrays, allowing query string parameter injection",
      "workarounds": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "\u003cp\u003eLeave `allowEmptyArrays` off (the default), or check key names that come from untrusted input against an allowlist before passing the object to `qs.stringify`.\u003c/p\u003e"
            }
          ],
          "value": "Leave `allowEmptyArrays` off (the default), or check key names that come from untrusted input against an allowlist before passing the object to `qs.stringify`."
        }
      ]
    }
  },
  "cveMetadata": {
    "assignerOrgId": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
    "assignerShortName": "harborist",
    "cveId": "CVE-2026-110910",
    "datePublished": "2026-10-27T06:42:42.365Z",
    "dateReserved": "2026-10-15T03:01:58.840Z",
    "dateUpdated": "2026-10-27T19:32:36.456Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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