CVE-2026-54335Low· 3.7▾ SunlitPrototype pollution in @feathersjs/commons _.merge via JSON-parsed __proto__
▾ Sunlit zone — Low / medium · no exploitation signal
impact 20.4 · likelihood 0.1 · exploitation 0
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Exploit-prediction probability, daily snapshots since Aug 2.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via GHSA
0.3%
0.3% → 0.4%
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.
Fixed in @feathersjs/[email protected]. The fix skips __proto__, constructor, and prototype keys during iteration — the standard remediation used by lodash and others.
Avoid passing JSON-parsed untrusted input through commons._.merge. Freezing Object.prototype or validating/sanitizing keys upstream also mitigates.
Reported responsibly by Andrew Ridings (@ridingsa).
@feathersjs/commons <= 5.0.44Upgrade to a patched release:
@feathersjs/commons 5.0.45Connected by shared product, vendor, weakness, or advisory.
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