Prototype pollution in protobuf.js - #VU136899
Published: July 4, 2026
Vulnerability identifier: #VU136899
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: N/A
CWE-ID: CWE-1321
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: protobuf.js
Affected software:
protobuf.js
protobuf.js
Detailed vulnerability description
The vulnerability allows a remote attacker to disclose sensitive information or modify application behavior.
The vulnerability exists due to improperly controlled modification of object prototype attributes in the text format string-keyed map parser when parsing attacker-supplied protobuf text-format input. A remote attacker can provide a crafted map entry with the key __proto__ to disclose sensitive information or modify application behavior.
Only the optional Text Format extension is affected. Exploitation requires a target schema with a string-keyed map field, and impact depends on downstream application logic treating inherited properties on the returned map object as meaningful.
Remediation
Install security update from vendor's website.