CVE-2026-84367
ADVISORY - githubSummary
Impact
Applications are affected only if a schema renames keys with a regular-expression source and a Joi.expression() / Joi.x() target that interpolates the pattern's own match data, combined with { multiple: true }, for example .rename(/^x-(.+)$/, Joi.x('{#1}'), { multiple: true }). Because the target is rendered from the matched input key, an attacker who controls input keys can send x-__proto__ with an object value and make the rename target render as __proto__, which sets the prototype of the object joi returns instead of creating a key on it. The global Object.prototype is not modified, so the effect is confined to the object returned by that one validate() call.
Schemas using a static string rename target are not affected, and neither are schemas left on the default { multiple: false }.
Patches
Versions 17.13.5 and 18.2.4 have been released to address the issue.
Workarounds
- Replace the template rename target with a static string target.
- Keep the template but make the capture unable to produce
__proto__, using a negative lookahead:.rename(/^x-(?!__proto__$)(.+)$/, Joi.x('{#1}'), { multiple: true }) - Drop { multiple: true } from the rename, which stops the rename before the assignment.
Common Weakness Enumeration (CWE)
Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
GitHub
2.2
CVSS SCORE
3.7low| Package | Type | OS Name | OS Version | Affected Ranges | Fix Versions |
|---|---|---|---|---|---|
| joi | npm | - | - | >=18.0.0,<18.2.4 | 18.2.4 |
| joi | npm | - | - | >=16.0.0,<17.13.5 | 17.13.5 |
CVSS:3 Severity and metrics
The CVSS metrics represent different qualitative aspects of a vulnerability that impact the overall score, as defined by the CVSS Specification.
The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone). One example of an Adjacent attack would be an ARP (IPv4) or neighbor discovery (IPv6) flood leading to a denial of service on the local LAN segment (e.g., CVE-2013-6014).
A successful attack depends on conditions beyond the attacker's control, requiring investing a measurable amount of effort in research, preparation, or execution against the vulnerable component before a successful attack.
The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
The vulnerable system can be exploited without interaction from any user.
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.
There is no loss of confidentiality.
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.
There is no impact to availability within the impacted component.
NIST
2.2