{"id":"DEBIAN-CVE-2026-110910","details":"### 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    - `\u003e=6.12.0 \u003c6.12.6`, fixed in v6.12.6    - `\u003e=6.13.0 \u003c6.13.4`, fixed in v6.13.4    - `\u003e=6.14.0 \u003c6.14.3`, fixed in v6.14.3    - `\u003e=6.15.0 \u003c6.15.4`, fixed in v6.15.4    - `\u003e=6.16.0 \u003c6.16.2`, 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.","modified":"2026-11-05T09:47:26.163152511Z","published":"2026-10-27T07:16:32.263Z","upstream":["CVE-2026-110910"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-110910"}],"affected":[{"package":{"name":"node-qs","ecosystem":"Debian:12","purl":"pkg:deb/debian/node-qs?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.11.0+ds+~6.9.7-3","6.11.0+ds+~6.9.7-4","6.13.0+ds+~6.9.16-1","6.14.1+ds+~6.14.0-1","6.15.0+ds+~6.15.0-1","6.15.0+ds+~6.15.0-2","6.15.0+ds+~6.15.0-3","6.15.2+ds+~6.15.1-1","6.16.0+ds+~6.15.1-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-110910.json"}},{"package":{"name":"node-qs","ecosystem":"Debian:13","purl":"pkg:deb/debian/node-qs?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.13.0+ds+~6.9.16-1","6.14.1+ds+~6.14.0-1","6.15.0+ds+~6.15.0-1","6.15.0+ds+~6.15.0-2","6.15.0+ds+~6.15.0-3","6.15.2+ds+~6.15.1-1","6.16.0+ds+~6.15.1-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-110910.json"}},{"package":{"name":"node-qs","ecosystem":"Debian:14","purl":"pkg:deb/debian/node-qs?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.13.0+ds+~6.9.16-1","6.14.1+ds+~6.14.0-1","6.15.0+ds+~6.15.0-1","6.15.0+ds+~6.15.0-2","6.15.0+ds+~6.15.0-3","6.15.2+ds+~6.15.1-1","6.16.0+ds+~6.15.1-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-110910.json"}}],"schema_version":"1.9.2","severity":[{"type":"CVSS_V4","score":"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"}]}