Prototype Pollution
CVE-2026-54335
LOW
GHSA-28xv-ph75-77wh
Severity by source
AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
DescriptionGitHub Advisory
Impact
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.
Patches
Fixed in @feathersjs/commons@5.0.45. The fix skips __proto__, constructor, and prototype keys during iteration - the standard remediation used by lodash and others.
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).
Analysis
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. …
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External POC / Exploit Code
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