CVE-2026-33994: Locutus Prototype Pollution due to incomplete fix for CVE-2026-25521
(updated )
A prototype pollution vulnerability exists in the parse_str function of the npm package locutus. An attacker can pollute Object.prototype by overriding RegExp.prototype.test and then passing a crafted query string to parse_str, bypassing the prototype pollution guard.
This vulnerability stems from an incomplete fix for CVE-2026-25521. The CVE-2026-25521 patch replaced the String.prototype.includes()-based guard with a RegExp.prototype.test()-based guard. However, RegExp.prototype.test is itself a writable prototype method that can be overridden, making the new guard bypassable in the same way as the original — trading one hijackable built-in for another.
References
- github.com/advisories/GHSA-vc8f-x9pp-wf5p
- github.com/locutusjs/locutus
- github.com/locutusjs/locutus/commit/345a6211e1e6f939f96a7090bfeff642c9fcf9e4
- github.com/locutusjs/locutus/pull/597
- github.com/locutusjs/locutus/releases/tag/v3.0.25
- github.com/locutusjs/locutus/security/advisories/GHSA-rxrv-835q-v5mh
- github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5p
- nvd.nist.gov/vuln/detail/CVE-2026-33994
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