How severe is CVE-2026-33993?

No CVSS score has been assigned to CVE-2026-33993 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-33993?

CVE-2026-33993 affects the following packages: locutus (npm). Ecosystems affected: npm.

How do I fix CVE-2026-33993?

Update locutus to 3.0.25 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-33993 is resolved across your whole dependency graph.

How do I detect CVE-2026-33993 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for locutus. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2026-33993 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2026-33993?

O3 pinpoints whether CVE-2026-33993 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2026-33993 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-33993 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-33993?

CVE-2026-33993 has an EPSS (Exploit Prediction Scoring System) score of 0.6%, placing it in the 43th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

When was CVE-2026-33993 published, and has it been updated?

CVE-2026-33993 was published on March 27, 2026 and was last updated on April 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

CVE-2026-33993

Locutus has Prototype Pollution via __proto__ Key Injection in unserialize()

Also known asGHSA-4mph-v827-f877

Published

Mar 27, 2026

Updated

Apr 10, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

EPSS Exploitation Probability

via FIRST.org ↗

0.6%probability of exploitation in next 30 days

Lower Risk43th percentile+0.53%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

1 pkg affected

📦locutus

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.

Description

Locutus brings stdlibs of other programming languages to JavaScript for educational purposes. Prior to version 3.0.25, the unserialize() function in locutus/php/var/unserialize assigns deserialized keys to plain objects via bracket notation without filtering the __proto__ key. When a PHP serialized payload contains __proto__ as an array or object key, JavaScript's __proto__ setter is invoked, replacing the deserialized object's prototype with attacker-controlled content. This enables property injection, for...in propagation of injected properties, and denial of service via built-in method override. This is distinct from the previously reported prototype pollution in parse_str (GHSA-f98m-q3hr-p5wq, GHSA-rxrv-835q-v5mh) — unserialize is a different function with no mitigation applied. Version 3.0.25 patches the issue.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`locutus`	all versions	3.0.25

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for locutus. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update locutus to 3.0.25 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-33993 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-33993 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2026-33993. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

Locutus brings stdlibs of other programming languages to JavaScript for educational purposes. Prior to version 3.0.25, the `unserialize()` function in `locutus/php/var/unserialize` assigns deserialized keys to plain objects via bracket notation without filtering the `__proto__` key. When a PHP serialized payload contains `__proto__` as an array or object key, JavaScript's `__proto__` setter is invoked, replacing the deserialized object's prototype with attacker-controlled content. This enables property injection, for...in propagation of injected properties, and denial of service via built-in m

O3 Security · Impact-Aware SCA

Is CVE-2026-33993 in your dependencies?

O3 detects CVE-2026-33993 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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