{"id":"GHSA-r5mx-6wc6-7h9w","summary":"dottie is vulnerable to Prototype Pollution bypass via non-first path segments in set() and transform()","details":"### Summary\n\ndottie versions 2.0.4 through 2.0.6 contain an incomplete fix for CVE-2023-26132. The prototype pollution guard introduced in commit `7d3aee1` only validates the first segment of a dot-separated path, allowing an attacker to bypass the protection by placing `__proto__` at any position other than the first.\n\nBoth `dottie.set()` and `dottie.transform()` are affected.\n\n### Details\n\nThe existing guard checks only `pieces[0] === '__proto__'`. When a path like `'a.__proto__.polluted'` is used, `pieces[0]` evaluates to `'a'`, not `'__proto__'`, so the guard is bypassed.\n\nInside the traversal loop, `current['__proto__'] = {}` triggers the `__proto__` setter, replacing the intermediate object's prototype. The final value is then written onto this new prototype.\n\n**Important distinction:** This vulnerability does NOT pollute the global `Object.prototype`. It injects properties into a specific object's prototype chain. However, injected properties are invisible to `hasOwnProperty()` and `Object.keys()`, which makes them difficult to detect and can lead to authorization bypass in common coding patterns.\n\n### PoC\n```javascript\nconst dottie = require('dottie');\n\n// set() bypass\nconst obj = {};\ndottie.set(obj, 'session.__proto__.isAdmin', true);\nconsole.log(obj.session.isAdmin);                    // true\nconsole.log(({}).isAdmin);                           // undefined\nconsole.log(obj.session.hasOwnProperty('isAdmin'));  // false\n\n// transform() bypass\nconst flat = { 'user.__proto__.role': 'admin', 'user.name': 'guest' };\nconst result = dottie.transform(flat);\nconsole.log(result.user.role);                       // 'admin'\nconsole.log(({}).role);                              // undefined\n```\n\nTested on Node.js v20 and v22, dottie 2.0.6, Windows 11.\n\n### Impact\n\nThe primary risk is authorization bypass. In a typical server-side scenario where dottie is used to process user input (e.g., via Sequelize, which depends on dottie with ~1.3M weekly npm downloads), an attacker can inject properties like `isAdmin: true` into objects used for access control decisions. Since the injected property is not an own property, standard checks using `hasOwnProperty()` or `Object.keys()` will not reveal it, while property access like `if (session.isAdmin)` will return `true`.\n\nAdditionally, replacing an object's prototype via `current['__proto__'] = {}` strips all inherited methods, potentially causing TypeError exceptions and denial of service.","aliases":["CVE-2026-27837"],"modified":"2026-03-13T08:27:14.502264Z","published":"2026-02-26T19:54:34Z","related":["CVE-2026-27837"],"database_specific":{"github_reviewed_at":"2026-02-26T19:54:34Z","nvd_published_at":"2026-02-26T01:16:24Z","cwe_ids":["CWE-1321"],"severity":"MODERATE","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/mickhansen/dottie.js/security/advisories/GHSA-r5mx-6wc6-7h9w"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-27837"},{"type":"WEB","url":"https://github.com/mickhansen/dottie.js/commit/7e8fa1345a4b46325f0eab8d7aeb1c4deaefdb14"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-4gxf-g5gf-22h4"},{"type":"PACKAGE","url":"https://github.com/mickhansen/dottie.js"}],"affected":[{"package":{"name":"dottie","ecosystem":"npm","purl":"pkg:npm/dottie"},"ranges":[{"type":"SEMVER","events":[{"introduced":"2.0.4"},{"fixed":"2.0.7"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 2.0.6","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/02/GHSA-r5mx-6wc6-7h9w/GHSA-r5mx-6wc6-7h9w.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L"}]}