CVE-2026-104183 stream-json: Prototype pollution: Assembler writes this.current[this.key] on plain objects
Attackers can pollute object prototypes via crafted JSON, potentially bypassing authorization checks or causing application errors in applications using the stream-json library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-104183?
CVE-2026-104183 is a medium-severity vulnerability in uhop stream-json, published on 1 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
stream-json is a micro-library of stream components for processing JSON and JSONC with a minimal memory footprint. Prior to 3.6.0, Assembler materializes object properties with plain assignment, so an input key named __proto__ invokes the inherited setter and causes parsed object prototype replacement instead of creating an own data property. Applications that make authorization or feature decisions from inherited values can therefore consume attacker-controlled properties, and a null prototype can disrupt code that expects Object.prototype methods. The researcher treats parsing untrusted JSON as part of the project contract, while the maintainer states that documented inputs are locally owned dumps, exports, or logs and characterizes the attack vector as local. The global Object.prototype is not polluted. This issue is fixed in version 3.6.0.
Weakness: CWE-1321
Which versions are affected by CVE-2026-104183?
2 open source packages ship an affected version, including stream-json.
| Package | Affected | Fixed in |
|---|---|---|
stream-json npm | All versions | 3.6.0 |
stream-json npm | All versions | 3.6.0 |
How do I fix CVE-2026-104183?
Upgrade stream-json to 3.6.0 or later.
Is CVE-2026-104183 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-104183 exists.
Sources
Also known as CLEANSTART-2026-ME44446, CLSA-2026-1791278816, GHSA-mjw6-4jj6-33hc.