CVE-2026-125117VulnerabilityPublished 10 Nov 2026

Mongoose walks into inherited properties when hydrating, setting, and merging, allowing overwrites of built-in

Affects mongooseSource GCVE Database

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Authoritative record:CVE-2026-125117· High 8.2

Not known to be exploited · CVSS 8.2 High : upgrade to 6.13.12 soon.

Data as of 10 Nov 2026, 23:24 UTC

CVSS 3.1 base score

8.2High

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 3.1	8.2

EPSS: 0.5% chance of exploitation in 30 days – higher than 48% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 6.13.12, 7.8.13, 8.24.7 +1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: Low
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 9 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 10 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
npmmongoose	Affected <6.13.12	Fixed in 6.13.12
npmmongoose	Affected >=7.0.0 <7.8.13	Fixed in 7.8.13
npmmongoose	Affected >=8.0.0 <8.24.7	Fixed in 8.24.7
npmmongoose	Affected >=9.0.0 <9.11.4	Fixed in 9.11.4

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

### Summary Three Mongoose code paths copy data into objects by property name without checking whether the property is the object's own or inherited from its prototype: 1. Loading a document from the database (`init()`, also used by `Model.hydrate()`) 2. Setting a dotted path on a document (`$__set`, used by `new Model(obj)`, `doc.set()` and `doc.$set()`) 3. Merging update documents (`utils.mergeClone`, used by `findOneAndReplace()`, chained update calls and `Query.prototype.merge()`) When a key names an inherited property, such as `toString` or `valueOf`, or a document internal such as `$__schema`, Mongoose writes into the shared object behind that property. The data comes from the attacker. - **Denial of service.** For example, `{ "toString": { "call": 1 } }` overwrites `Object.prototype.toString.call`. Mongoose and most other libraries rely on `Object.prototype.toString.call()`. After the overwrite, every later query in the process throws `TypeError: _toString.call is not a function` until the process restarts. This includes queries on unrelated models. - **Changing shared schema state.** Through a subdocument with `strict: false`, a path such as `profile.$__schema.paths.email.validators` reaches the subdocument's schema, which every document shares. Setting it to `[]` removes the `required` validator for every document in the process. Mongoose already blocked `__proto__`, `constructor` and `prototype`, so these bugs cannot add properties to `Object.prototype` itself. They can still overwrite methods and properties of shared built-in functions and of Mongoose's internal objects. ### Details #### 1. Loading documents: `init()` ```js if (!schemaType && utils.isPOJO(value)) { // assume nested object if (!doc[i]) { doc[i] = {}; ... } init(self, value, doc[i], opts, path + '.'); } ``` For a stored field named `toString`, `doc[i]` is the inherited `Object.prototype.toString`. It is truthy, so `init()` recurses into that function and copies the stored subfields onto it. This runs for every document Mongoose loads: `find()`, `findOne()`, cursors, populated documents and `Model.hydrate()`. It runs whatever the `strict` setting, and it applies to top-level and nested paths alike. `lean()` queries are not affected. A malicious document can get into the collection in several ways: - through a model with `strict: false`, for example `new Model(req.body).save()`; - through another application or the raw MongoDB driver; - through any update that writes arbitrary keys. #### 2. Setting dotted paths: `$__set` When it walks a dotted path, `$__set` read `obj[parts[i]]` and descended into whatever it found. That included inherited functions, such as `Object.prototype.toString` on a plain object or `Document.prototype.toObject` on a subdocument. On subdocuments it also included non-function internals that are prototype getters, such as `$__schema`, `schema`, `$__middleware` and `$__schemaTypeOptions`. Those point at objects that every document of the model shares. Attacker-controlled input reaches this path through: - **A `Mixed` path on a default, strict schema:** `new Model({ "mixed.toString.call": 1 })`, or `doc.set({ "mixed.toString.call": 1 })`. Nothing needs to be saved. - **Any root path on a schema with `strict: false`:** for example `doc.set('toString.call', 1)`. - **A subdocument with `strict: false`**, when the application passes a user-controlled path to `doc.set(path, value)`: for example `doc.set('profile.$__schema.paths.email.validators', [])`. #### 3. Merging updates: `utils.mergeClone` ```js if (typeof to[key] === 'undefined') { to[key] = clone(fromObj[key]); } else if (isObject(val)) { mergeClone(to[key], val); // to[key] may be an inherited built-in } ``` `to[key]` was read without an own-property check, so a key such as `toString` recursed into `Object.prototype.toString`. This affects: - **`Model.findOneAndReplace(filter, replacement)`.** It always merges the replacement into the query's update, so a single call with an untrusted replacement is enough. - **Update calls chained onto a query that already has an update.** For example `Model.updateOne(filter, { $set: {...} }).updateOne({}, untrustedUpdate)`, the same pattern with `findOneAndUpdate()`, or middleware that calls `this.updateOne(...)`. - **`Query.prototype.merge()`** with a source query whose update came from untrusted input. ### Proof of concept ```js const mongoose = require('mongoose'); const { Schema } = mongoose; // 2. Setting dotted paths: a Mixed path on a default strict schema, nothing saved const Item = mongoose.model('Item', new Schema({ name: String, meta: {} })); new Item(JSON.parse('{"meta.toString.call": 1}')); // e.g. new Item(req.body) console.log(typeof Object.prototype.toString.call); // 'number' // From here on, every query in the process fails: // TypeError: _toString.call is not a function ``` ```js // 1. Loading documents: a stored field named after an Object.prototype method const Loose =

CWE-1321Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution) (opens in a new tab)
Variant weakness
The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.
Implementation
By freezing the object prototype first (for example, Object.freeze(Object.prototype)), modification of the prototype becomes impossible.
Architecture and Design
By blocking modifications of attributes that resolve to object prototype, such as proto or prototype, this weakness can be mitigated.
Implementation · Input Validation
When handling untrusted objects, validating using a schema can be used.
OWASP Cheat Sheets
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V5.1.2 (opens in a new tab)
Attack patterns
Accessing Functionality Not Properly Constrained by ACLs (opens in a new tab)
Exploiting Incorrectly Configured Access Control Security Levels (opens in a new tab)
Manipulating User-Controlled Variables (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

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Affected software

Description

WeaknessesCWE-1321

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