CVE-2026-110910 (GCVE-0-2026-110910)

Vulnerability from cvelistv5 – Published: 2026-10-27 06:42 – Updated: 2026-10-27 19:32
VLAI
Title
qs.stringify with allowEmptyArrays does not encode the keys of empty arrays, allowing query string parameter injection
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.
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
Assigner
harborist CNA under the redhat root
CNA scorecard B 85/100 over 14 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
ljharb qs Affected: 6.12.0 , < 6.12.6 (semver)
Affected: 6.13.0 , < 6.13.4 (semver)
Affected: 6.14.0 , < 6.14.3 (semver)
Affected: 6.15.0 , < 6.15.4 (semver)
Affected: 6.16.0 , < 6.16.2 (semver)
guessed Create a notification for this product.
Credits
DucMinhNe DucMinhNe ljharb
Show details on NVD website
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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"
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          {
            "lang": "en",
            "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."
          }
        ],
        "id": "CVE-2026-110910",
        "lastModified": "2026-10-27T20:17:12.297",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "HIGH",
                "attackVector": "NETWORK",
                "availabilityImpact": "NONE",
                "baseScore": 3.7,
                "baseSeverity": "LOW",
                "confidentialityImpact": "NONE",
                "integrityImpact": "LOW",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N",
                "version": "3.1"
              },
              "exploitabilityScore": 2.2,
              "impactScore": 1.4,
              "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
              "type": "Secondary"
            }
          ],
          "cvssMetricV40": [
            {
              "cvssData": {
                "Automatable": "NOT_DEFINED",
                "Recovery": "NOT_DEFINED",
                "Safety": "NOT_DEFINED",
                "attackComplexity": "LOW",
                "attackRequirements": "PRESENT",
                "attackVector": "NETWORK",
                "availabilityRequirement": "NOT_DEFINED",
                "baseScore": 6.3,
                "baseSeverity": "MEDIUM",
                "confidentialityRequirement": "NOT_DEFINED",
                "exploitMaturity": "NOT_DEFINED",
                "integrityRequirement": "NOT_DEFINED",
                "modifiedAttackComplexity": "NOT_DEFINED",
                "modifiedAttackRequirements": "NOT_DEFINED",
                "modifiedAttackVector": "NOT_DEFINED",
                "modifiedPrivilegesRequired": "NOT_DEFINED",
                "modifiedSubAvailabilityImpact": "NOT_DEFINED",
                "modifiedSubConfidentialityImpact": "NOT_DEFINED",
                "modifiedSubIntegrityImpact": "NOT_DEFINED",
                "modifiedUserInteraction": "NOT_DEFINED",
                "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
                "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
                "modifiedVulnIntegrityImpact": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
                "version": "4.0",
                "vulnAvailabilityImpact": "NONE",
                "vulnConfidentialityImpact": "NONE",
                "vulnIntegrityImpact": "LOW",
                "vulnerabilityResponseEffort": "NOT_DEFINED"
              },
              "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
              "type": "Secondary"
            }
          ]
        },
        "published": "2026-10-27T07:16:32.263",
        "references": [
          {
            "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
            "url": "https://github.com/ljharb/qs/commit/033526fc82f2e80a3d896df2bce9137e34cb5dc5"
          },
          {
            "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
            "url": "https://github.com/ljharb/qs/commit/234d5051f5071efaa025a7ca9e4d34a56a460a1b"
          },
          {
            "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
            "url": "https://github.com/ljharb/qs/commit/5d3b1b9ec6afd0cfc760c8e12862873789a32fc8"
          },
          {
            "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
            "url": "https://github.com/ljharb/qs/commit/6b8bf1a53d7b0c5e7e434eaae8e2c0cffd5c2492"
          },
          {
            "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
            "url": "https://github.com/ljharb/qs/commit/ad445aa23e4c3a97394c3b9a5f9d7a7159eb1f17"
          },
          {
            "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
            "url": "https://github.com/ljharb/qs/commit/f9dd4830cb922363822cdfdca2cceb3ed9792224"
          },
          {
            "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
            "url": "https://github.com/ljharb/qs/issues/626"
          },
          {
            "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
            "url": "https://github.com/ljharb/qs/pull/561"
          },
          {
            "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
            "url": "https://github.com/ljharb/qs/security/advisories/GHSA-w4cr-vjpx-p82q"
          }
        ],
        "sourceIdentifier": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
        "vulnStatus": "Awaiting Analysis",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-116"
              }
            ],
            "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
            "type": "Secondary"
          }
        ]
      }
    }
  }
}



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