CVE-2025-62517: Rollbar.js Prototype Pollution Vulnerability

CVE-2025-62517 Overview

CVE-2025-62517 is a prototype pollution vulnerability in Rollbar.js, a JavaScript library that provides error tracking and logging to the Rollbar service. The flaw exists in the merge() function and affects versions before 2.26.5, as well as versions from 3.0.0-alpha1 up to but not including 3.0.0-beta5. Applications that pass untrusted input to rollbar.configure() allow attackers to pollute the Object prototype. The vulnerability is classified under [CWE-1321] Improperly Controlled Modification of Object Prototype Attributes. Rollbar addressed the issue in versions 2.26.5 and 3.0.0-beta5.

Critical Impact
Attackers who control input to rollbar.configure() can inject properties into Object.prototype, potentially altering application logic, bypassing security checks, or enabling downstream exploitation.

Affected Products

Rollbar.js versions prior to 2.26.5
Rollbar.js versions 3.0.0-alpha1 through 3.0.0-beta4
JavaScript applications invoking rollbar.configure() with attacker-controlled data

Discovery Timeline

2025-10-23 - CVE-2025-62517 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-62517

Vulnerability Analysis

Rollbar.js exposes a merge() utility used internally to combine configuration objects when rollbar.configure() is invoked. The function recursively copied properties from a source object into a target without filtering dangerous keys such as __proto__, constructor, or prototype. An attacker who supplies a crafted object to rollbar.configure() can therefore write arbitrary properties onto Object.prototype, affecting every object in the JavaScript runtime.

Exploitation requires the application to forward untrusted input into the Rollbar configuration call, which raises attack complexity. Once pollution occurs, the impact is limited to integrity, since the attacker manipulates object state rather than reading sensitive data or crashing the process directly.

Root Cause

The merge() implementation in src/merge.js initialized its accumulator as result = {}, inheriting from Object.prototype. Combined with a _set() helper in src/utility.js that walked dotted key paths without sanitization, this allowed writes to __proto__.polluted and similar chains. The absence of key filtering or prototype-safe object construction is the primary defect.

Attack Vector

The attack is network-reachable when applications pass user-controlled JSON — for example, values sourced from query parameters, request bodies, or client-side postMessage — directly into rollbar.configure(). No authentication or user interaction is required, though the attack complexity is high because it depends on the host application's data handling.

javascript

// Security patch in src/merge.js (from PR #1390 / #1394)
     copy,
     clone,
     name,
-    result = {},
+    result = Object.create(null), // no prototype pollution on Object
     current = null,
     length = arguments.length;

Source: rollbar/rollbar.js commit 61032fe

javascript

// Security patch in src/utility.js (from PR #1390 / #1394)
   if (!obj) {
     return;
   }
+
+  // Prevent prototype pollution by setting the prototype to null.
+  Object.setPrototypeOf(obj, null);
+
   var keys = path.split('.');
   var len = keys.length;
   if (len < 1) {

Source: rollbar/rollbar.js commit d717def

The fix replaces the plain object literal with Object.create(null), producing an accumulator with no prototype chain, and calls Object.setPrototypeOf(obj, null) before traversing dotted key paths.

Detection Methods for CVE-2025-62517

Indicators of Compromise

Presence of rollbar.js at versions below 2.26.5 or between 3.0.0-alpha1 and 3.0.0-beta4 in application dependencies or package-lock.json
Runtime properties appearing on Object.prototype that were not defined by the application
HTTP request payloads containing keys such as __proto__, constructor, or prototype reaching endpoints that pass data to rollbar.configure()

Detection Strategies

Run software composition analysis (SCA) against JavaScript dependencies to flag vulnerable Rollbar.js versions.
Audit application source code for any call to rollbar.configure() that accepts input derived from HTTP requests, cookies, or client-supplied JSON.
Add runtime assertions or tests that verify Object.prototype is not modified after configuration.

Monitoring Recommendations

Log and alert on inbound HTTP payloads containing __proto__ or constructor.prototype key patterns at the WAF or application gateway.
Track deployments of Rollbar.js through your package registry and continuous integration pipelines to identify unpatched builds.
Monitor error telemetry for unexpected TypeError or property access anomalies that may indicate prototype tampering.

How to Mitigate CVE-2025-62517

Immediate Actions Required

Upgrade Rollbar.js to version 2.26.5 for the 2.x branch, or 3.0.0-beta5 or later for the 3.x branch.
Identify and refactor any code path where rollbar.configure() receives values derived from untrusted sources.
Rebuild and redeploy front-end bundles and Node.js services that ship the vulnerable library.

Patch Information

The fix was delivered in Rollbar.js 2.26.5 and 3.0.0-beta5 through pull requests #1390 and #1394. Details are documented in GitHub Security Advisory GHSA-xcg2-9pp4-j82x. Both patches replace mutable object accumulators with prototype-less objects created via Object.create(null) and strip the prototype chain from targets of _set().

Workarounds

Ensure values passed to rollbar.configure() never contain untrusted input; sanitize or allow-list configuration keys before invocation.
Filter reserved keys such as __proto__, constructor, and prototype from any object derived from user input before use.
Freeze Object.prototype at application startup with Object.freeze(Object.prototype) where compatible with dependencies.

bash

# Upgrade to a patched Rollbar.js release
npm install rollbar@2.26.5
# or, for the 3.x branch
npm install rollbar@3.0.0-beta5

# Verify installed version
npm ls rollbar