CVE-2026-54335

Prototype pollution in @feathersjs/commons _.merge via JSON-parsed proto

Workarounds

Avoid passing JSON-parsed untrusted input through commons._.merge. Freezing Object.prototype or validating/sanitizing keys upstream also mitigates.

Credit

Reported responsibly by Andrew Ridings (@ridingsa).

The _.merge(target, source) utility exported by @feathersjs/commons recursively merges source into target by iterating Object.keys(source). When source was produced by JSON.parse and contains a __proto__ (or constructor / prototype) key, that key is returned as an own-enumerable property. The recursive merge then resolves target['__proto__'] to Object.prototype and writes the attacker-supplied properties onto it, polluting the prototype for all plain objects in the process for the lifetime of the Node process.

Scope of real-world risk is limited. No first-party Feathers package routes input, trusted or untrusted, through commons._.merge. The @feathersjs/authentication package, which does merge request-influenced data, uses lodash/merge (prototype-pollution-safe since 4.17.12), not this utility. Exploitation therefore requires a downstream plugin or application to pass JSON-parsed, attacker-controlled input directly through the exported _.merge.

CVE-2026-54335 has a CVSS score of 3.7 (Low). The vector is network-reachable, no 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 (5.0.45); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Fixed in @feathersjs/[email protected]. The fix skips __proto__, constructor, and prototype keys during iteration, the standard remediation used by lodash and others.

1. What is CVE-2026-54335? CVE-2026-54335 is a low-severity security vulnerability in @feathersjs/commons (npm), affecting versions <= 5.0.44. It is fixed in 5.0.45.
2. How severe is CVE-2026-54335? CVE-2026-54335 has a CVSS score of 3.7 (Low). 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.
3. Which versions of @feathersjs/commons are affected by CVE-2026-54335? @feathersjs/commons (npm) versions <= 5.0.44 is affected.
4. Is there a fix for CVE-2026-54335? Yes. CVE-2026-54335 is fixed in 5.0.45. Upgrade to this version or later.
5. Is CVE-2026-54335 exploitable, and should I be worried? Whether CVE-2026-54335 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
6. What actually determines whether CVE-2026-54335 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.
7. How do I fix CVE-2026-54335? Upgrade @feathersjs/commons to 5.0.45 or later.