VulnerabilityPublished 29 May 2026Updated 2 Jun 2026

CVE-2026-46510: kaspernj form-data-objectizer · Prototype Pollution

Affects kaspernj form-data-objectizerSource CVE Database V5

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Not known to be exploited · CVSS 8.2 High : upgrade to 1.0.1 soon.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score

8.2High

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 20% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.0.1

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

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

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: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 29 May 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 29 Oct 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 kaspernj form-data-objectizer to 1.0.1.

Affected software

Product	Affected	Fixed in
kaspernjform-data-objectizer	Affected <1.0.1	Fixed in 1.0.1
npmform-data-objectizer`pkg:npm/form-data-objectizer`Other threats	Affected <1.0.1	Fixed in 1.0.1

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

AI-suggested

Upgrade the kaspernj form-data-objectizer library to version 1.0.1 or later, where this prototype pollution vulnerability is fixed. Avoid using vulnerable versions (<1.0.1) in production environments. Patch status is not explicitly confirmed beyond the version fix, so check the vendor advisory for the latest remediation guidance.

Description

form-data-objectizer converts FormData to object. Prior to 1.0.1, form-data-objectizer walks bracket-notation form keys (e.g.name[sub]) into nested objects without filtering __proto__, constructor, or prototype. A single HTTP form field whose name starts with __proto__[...] causes the library to mutate Object.prototype, which is a prototype pollution primitive of the entire Node.js process. This vulnerability is fixed in 1.0.1.

Impact

Exploitation of this vulnerability allows an attacker to modify the Object.prototype in the Node.js environment where the vulnerable form-data-objectizer library is used. This can lead to unexpected behavior or security issues in applications relying on object prototypes, potentially affecting integrity and availability. The CVSS score of 8.2 reflects a high severity due to the network attack vector, no required privileges or user interaction, and a high impact on integrity with some impact on availability. Confidentiality is not impacted.

Summary

The kaspernj form-data-objectizer library versions before 1.0.1 improperly handle bracket-notation form keys by not filtering out __proto__, constructor, or prototype keys. This flaw enables an attacker to perform prototype pollution by submitting form fields with names starting with __proto__[...], which mutates Object.prototype. Such mutation can lead to widespread impact on the Node.js process using this library. The issue is classified under CWE-1321 and has been assigned CVE-2026-46510. The vulnerability is resolved in version 1.0.1 of the library.

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).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 5 Jun 2026, 20:52 UTC

WeaknessesCWE-1321

Technical details

References

Community reviews

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