{"id":"CVE-2026-106448","aliases":["EUVD-2026-93973","GHSA-w48f-fwg7-ww6p"],"status":"published","title":"StableLib: Prototype poisoning via `__proto__` map keys in CBOR decoding","description":"StableLib is a stable library of useful TypeScript and JavaScript code. Prior to 2.0.4, the @stablelib/cbor CBOR map decoding path creates ordinary JavaScript objects and assigns attacker-controlled keys with bracket assignment. A map key named __proto__ invokes the inherited prototype setter instead of creating an ordinary own property, allowing the decoded object's prototype to contain attacker-controlled authorization or feature-flag values. Downstream code that trusts normal property lookup or merges the decoded object can therefore make security-sensitive decisions using inherited attacker data. This issue is fixed in version 2.0.4.","severity":{"version":"4.0","score":8.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-12","score":0.00401,"percentile":0.34837,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-1321"],"published":"2026-04-04T04:24:27Z","modified":"2026-10-28T02:30:37Z","fixes":[{"ecosystem":"npm","package":"@stablelib/cbor","fixed_in":["2.0.3"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"npm","package":"@stablelib/cbor","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.0.3"}]}]},{"source":"osv","ecosystem":"npm","package":"@stablelib/cbor","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.0.3"}]}]}],"products":[{"vendor":"stablelib","product":"stablelib"}],"references":[{"url":"https://github.com/StableLib/stablelib/security/advisories/GHSA-w48f-fwg7-ww6p","tags":["x_refsource_CONFIRM","advisory","web"]},{"url":"https://github.com/StableLib/stablelib/commit/0f153a63b7552a0e8721f640984113e419015026","tags":["x_refsource_MISC","fix","web"]},{"url":"https://github.com/StableLib/stablelib/releases/tag/@stablelib/cbor@2.0.4","tags":["x_refsource_MISC","web"]},{"url":"https://github.com/advisories/GHSA-w48f-fwg7-ww6p"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/106xxx/CVE-2026-106448.json","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-106448","tags":["advisory"]},{"url":"https://github.com/StableLib/stablelib","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-106448","title":"StableLib: Prototype poisoning via `__proto__` map keys in CBOR decoding","description":"StableLib is a stable library of useful TypeScript and JavaScript code. Prior to 2.0.4, the @stablelib/cbor CBOR map decoding path creates ordinary JavaScript objects and assigns attacker-controlled keys with bracket assignment. A map key named __proto__ invokes the inherited prototype setter instead of creating an ordinary own property, allowing the decoded object's prototype to contain attacker-controlled authorization or feature-flag values. Downstream code that trusts normal property lookup or merges the decoded object can therefore make security-sensitive decisions using inherited attacker data. This issue is fixed in version 2.0.4.","status":"published","published":"2026-10-06T19:45:02.616Z","modified":"2026-10-07T17:07:38.703Z","cvss":[{"version":"4.0","score":8.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N","level":"high","assessor":"cna"}],"cwes":["CWE-1321"],"updated_at":"2026-11-02T14:20:04.156238Z"}],"euvd":[{"id":"EUVD-2026-93973","description":"StableLib is a stable library of useful TypeScript and JavaScript code. Prior to 2.0.4, the @stablelib/cbor CBOR map decoding path creates ordinary JavaScript objects and assigns attacker-controlled keys with bracket assignment. A map key named __proto__ invokes the inherited prototype setter instead of creating an ordinary own property, allowing the decoded object's prototype to contain attacker-controlled authorization or feature-flag values. Downstream code that trusts normal property lookup or merges the decoded object can therefore make security-sensitive decisions using inherited attacker data. This issue is fixed in version 2.0.4.","status":"published","published":"2026-10-06T19:45:02Z","modified":"2026-10-07T17:07:38Z","cvss":[{"version":"4.0","score":8.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N","level":"high"}],"updated_at":"2026-11-02T17:27:34.815018Z"}],"ghsa":[{"id":"GHSA-w48f-fwg7-ww6p","title":"@stablelib/cbor: Prototype poisoning via `__proto__` map keys in CBOR decoding","description":"### Summary\n\n`@stablelib/cbor` decodes CBOR maps into ordinary JavaScript objects and assigns attacker-controlled keys directly onto those objects. A CBOR map key named `__proto__` therefore changes the prototype of the decoded object instead of becoming an ordinary data property.\n\n### Details\n\nThe decoder builds map results with a plain `{}` and then stores attacker-controlled keys using bracket assignment.\n\nThat is unsafe for special property names. In JavaScript, assigning to `obj[\"__proto__\"]` on a normal object does not create a plain own property. It invokes the built-in `__proto__` setter and replaces the object’s prototype if the supplied value is an object or `null`.\n\nAs a result, a CBOR payload containing a map entry like:\n\n* key: `\"__proto__\"`\n* value: `{ isAdmin: true }`\n\ndoes not decode to an object with an own property called `__proto__`. It decodes to an object whose prototype is now attacker-controlled. Any code that later reads properties through normal lookup will see inherited attacker-supplied values.\n\n### PoC\n\n```js\nimport { decode } from \"@stablelib/cbor\";\n\n// CBOR:\n// {\n//   \"__proto__\": { \"isAdmin\": true }\n// }\n//\n// a1                    map(1)\n//   69                  text(9)\n//     \"__proto__\"\n//   a1                  map(1)\n//     67                text(7)\n//       \"isAdmin\"\n//     f5                true\n\nconst payload = new Uint8Array([\n  0xa1,\n  0x69, 0x5f, 0x5f, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x5f, 0x5f,\n  0xa1,\n  0x67, 0x69, 0x73, 0x41, 0x64, 0x6d, 0x69, 0x6e,\n  0xf5\n]);\n\nconst obj = decode(payload);\n\nconsole.log(Object.hasOwn(obj, \"isAdmin\")); // false\nconsole.log(obj.isAdmin);                   // true\nconsole.log(Object.getPrototypeOf(obj).isAdmin); // true\n```\n\n### Impact\n\nAny application that decodes untrusted CBOR into JavaScript objects can receive objects with attacker-controlled prototypes.\n\nIn practice, that can corrupt configuration objects, influence authorization checks, alter feature flags, and break application logic that relies on normal property lookup instead of strict own-property checks. If the decoded object is later merged into other objects, the impact can spread further.\n\n### Solution\n\nUpgrade to version 2.0.4.","status":"published","published":"2026-04-04T04:24:27Z","modified":"2026-04-07T14:23:13Z","cvss":[{"version":"4.0","score":8.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N","level":"high"}],"cwes":["CWE-1321"],"updated_at":"2026-11-02T14:39:50.076383Z"}],"nvd":[{"id":"CVE-2026-106448","description":"StableLib is a stable library of useful TypeScript and JavaScript code. Prior to 2.0.4, the @stablelib/cbor CBOR map decoding path creates ordinary JavaScript objects and assigns attacker-controlled keys with bracket assignment. A map key named __proto__ invokes the inherited prototype setter instead of creating an ordinary own property, allowing the decoded object's prototype to contain attacker-controlled authorization or feature-flag values. Downstream code that trusts normal property lookup or merges the decoded object can therefore make security-sensitive decisions using inherited attacker data. This issue is fixed in version 2.0.4.","status":"published","published":"2026-10-06T20:17:26.743Z","modified":"2026-10-07T17:16:47.727Z","cvss":[{"version":"4.0","score":8.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/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","level":"high","assessor":"secondary"}],"cwes":["CWE-1321"],"updated_at":"2026-11-02T14:12:54.809359Z"}],"osv":[{"id":"CVE-2026-106448","title":"StableLib: Prototype poisoning via `__proto__` map keys in CBOR decoding","description":"StableLib is a stable library of useful TypeScript and JavaScript code. Prior to 2.0.4, the @stablelib/cbor CBOR map decoding path creates ordinary JavaScript objects and assigns attacker-controlled keys with bracket assignment. A map key named __proto__ invokes the inherited prototype setter instead of creating an ordinary own property, allowing the decoded object's prototype to contain attacker-controlled authorization or feature-flag values. Downstream code that trusts normal property lookup or merges the decoded object can therefore make security-sensitive decisions using inherited attacker data. This issue is fixed in version 2.0.4.","status":"published","published":"2026-10-06T19:45:02.616Z","modified":"2026-10-28T02:30:37.281298979Z","cvss":[{"version":"4.0","score":8.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N","level":"high"}],"cwes":["CWE-1321"],"updated_at":"2026-11-02T15:44:54.583213Z"},{"id":"GHSA-w48f-fwg7-ww6p","title":"@stablelib/cbor: Prototype poisoning via `__proto__` map keys in CBOR decoding","description":"### Summary\n\n`@stablelib/cbor` decodes CBOR maps into ordinary JavaScript objects and assigns attacker-controlled keys directly onto those objects. A CBOR map key named `__proto__` therefore changes the prototype of the decoded object instead of becoming an ordinary data property.\n\n### Details\n\nThe decoder builds map results with a plain `{}` and then stores attacker-controlled keys using bracket assignment.\n\nThat is unsafe for special property names. In JavaScript, assigning to `obj[\"__proto__\"]` on a normal object does not create a plain own property. It invokes the built-in `__proto__` setter and replaces the object’s prototype if the supplied value is an object or `null`.\n\nAs a result, a CBOR payload containing a map entry like:\n\n* key: `\"__proto__\"`\n* value: `{ isAdmin: true }`\n\ndoes not decode to an object with an own property called `__proto__`. It decodes to an object whose prototype is now attacker-controlled. Any code that later reads properties through normal lookup will see inherited attacker-supplied values.\n\n### PoC\n\n```js\nimport { decode } from \"@stablelib/cbor\";\n\n// CBOR:\n// {\n//   \"__proto__\": { \"isAdmin\": true }\n// }\n//\n// a1                    map(1)\n//   69                  text(9)\n//     \"__proto__\"\n//   a1                  map(1)\n//     67                text(7)\n//       \"isAdmin\"\n//     f5                true\n\nconst payload = new Uint8Array([\n  0xa1,\n  0x69, 0x5f, 0x5f, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x5f, 0x5f,\n  0xa1,\n  0x67, 0x69, 0x73, 0x41, 0x64, 0x6d, 0x69, 0x6e,\n  0xf5\n]);\n\nconst obj = decode(payload);\n\nconsole.log(Object.hasOwn(obj, \"isAdmin\")); // false\nconsole.log(obj.isAdmin);                   // true\nconsole.log(Object.getPrototypeOf(obj).isAdmin); // true\n```\n\n### Impact\n\nAny application that decodes untrusted CBOR into JavaScript objects can receive objects with attacker-controlled prototypes.\n\nIn practice, that can corrupt configuration objects, influence authorization checks, alter feature flags, and break application logic that relies on normal property lookup instead of strict own-property checks. If the decoded object is later merged into other objects, the impact can spread further.\n\n### Solution\n\nUpgrade to version 2.0.4.","status":"published","published":"2026-04-04T04:24:27Z","modified":"2026-10-07T10:56:10.181649137Z","cvss":[{"version":"4.0","score":8.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N","level":"high"}],"cwes":["CWE-1321"],"updated_at":"2026-11-02T15:46:58.04805Z"}]}}