Prototype Pollution in Uhop Stream-Json

CVE-2026-104183

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.

Vulnerability class: Prototype Pollution

Published .

CVSS v3 metric

CVSS v3 base score 5.1 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-104183?
CVE-2026-104183 is a medium-severity vulnerability in Uhop Stream-Json, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 5.1/10. Published 2026-10-01.
How severe is CVE-2026-104183?
Medium severity. CVSS v3 base score is 5.1 out of 10.