{"id":"DEBIAN-CVE-2026-82417","details":"### Summary    `qs.stringify` throws a `TypeError` when it serializes an object whose own `constructor` property has a truthy, non-callable `isBuffer` member. `utils.isBuffer` duck-types buffers by calling `obj.constructor.isBuffer(obj)` after checking only that the property is truthy, so a value such as `{ constructor: { isBuffer: \"x\" } }` makes the call throw `TypeError: obj.constructor.isBuffer is not a function`.    ### Details    `lib/stringify.js:127` calls `utils.isBuffer` on every non-primitive value it serializes. `utils.isBuffer` (`lib/utils.js:332`) reads `obj.constructor.isBuffer` and invokes it without verifying that it is a function. `constructor` and `isBuffer` are ordinary property names, so any object carrying them as own properties reaches the unchecked call.    Such an object can be built from untrusted input. `qs.parse(\"x[constructor][isBuffer]=y\", { plainObjects: true })` or `{ allowPrototypes: true }` keeps the `constructor` key as an own property (the default parse options drop it), and `JSON.parse(\"{\\\"a\\\":{\\\"constructor\\\":{\\\"isBuffer\\\":\\\"x\\\"}}}\")` produces the same shape with no qs option involved. Express 4 with its default `query parser` setting and body-parser with `extended: true` both call `qs.parse` with `allowPrototypes: true`, so on those stacks `req.query` and `req.body` can carry the shape directly.    #### PoC    ```js    var qs = require(\"qs\");    qs.stringify(qs.parse(\"x[constructor][isBuffer]=y\", { plainObjects: true }));    qs.stringify(JSON.parse(\"{\\\"a\\\":{\\\"constructor\\\":{\\\"isBuffer\\\":\\\"x\\\"}}}\"));    // TypeError: obj.constructor.isBuffer is not a function    //     at Object.isBuffer (lib/utils.js:332:78)    //     at stringify (lib/stringify.js:127:45)    ```    #### Fix    `lib/utils.js`, applied in e83d321 on `main` and released as v6.16.0:    ```diff    - return !!(obj.constructor && obj.constructor.isBuffer && obj.constructor.isBuffer(obj));    + return !!(obj.constructor && typeof obj.constructor.isBuffer === \"function\" && obj.constructor.isBuffer(obj));    ```    Real `Buffer`, `safer-buffer`, and browserify `buffer` polyfill instances serialize exactly as before; only the throw is removed.    ### Affected versions    `\u003e=2.2.5 \u003c6.16.0`, fixed in v6.16.0.    The unguarded duck-type was introduced in 3768a75 and first shipped in v2.2.5 (September 2014). v2.2.4 and earlier used `Buffer.isBuffer` and are not affected. Every release from v2.2.5 through v6.15.3 contains the unguarded call.    ### Impact    An unauthenticated request can make any code path that re-serializes attacker-influenced data with `qs.stringify` (for example, rebuilding a query string from `req.query` for a redirect or an upstream request, or serializing a parsed JSON body) throw synchronously. In a typical Node.js HTTP framework the throw is caught by the framework error boundary and the affected request returns a 500; the process survives and other requests are unaffected. Where the call runs outside an error boundary, such as an `async` Express 4 handler (where the throw becomes an unhandled promise rejection) or a background job, the process exits, so the impact in that case depends on the application error handling rather than on qs.","modified":"2026-09-29T11:03:17.640800975Z","published":"2026-08-30T00:16:34.657Z","upstream":["CVE-2026-82417"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-82417"}],"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/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-82417.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/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-82417.json"}},{"package":{"name":"node-qs","ecosystem":"Debian:14","purl":"pkg:deb/debian/node-qs?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.16.0+ds+~6.15.1-1"}]}],"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"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-82417.json"}}],"schema_version":"1.9.0"}