CVE-2026-33993: Locutus brings stdlibs of other programming languages to JavaScript for educational purposes

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CRITICAL 9.8REMOTEUPGRADE

CVE-2026-33993 is a critical-severity flaw (CVSS 9.8) affecting locutus. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 prototyp

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 52%)
CISA exploited list	No
Weakness	CWE-1321
Published	2026-03-27
Last modified	2026-10-26

Publisher (CNA): GitHub, Inc. · Vendor: locutus

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-27 23:17 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

locutus locutus UPGRADE

Affected: < 3.0.25

Fixed in: 3.0.25

Safe to downgrade to: no unaffected older release

1. Check installed version

npm ls locutus

2. UPGRADE to 3.0.25

npm install locutus@">=3.0.25"

Exact fixes by distribution

npm · locutus · FIXED · 3.0.25 · vulnerable: < 3.0.25 · source

npm install locutus@">=3.0.25" npm ls locutus

Fedora ELN · rust-snpguest · FIXED · 0.11.0-1.eln159 · FEDORA-2026-baa01ba6c8 · source

sudo dnf upgrade --advisory=FEDORA-2026-baa01ba6c8

Fedora 46 · rust-sev · FIXED · 8.0.0-1.fc46 · FEDORA-2026-df06b5fb0c · source

sudo dnf upgrade --advisory=FEDORA-2026-df06b5fb0c

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Write-up: github.com/locutusjs/locutus/security/advisories/GHSA-4mph-v827-f877

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-33993?

locutus: upgrade to 3.0.25. Exact commands for each OS are on this page.

Is CVE-2026-33993 being exploited?

CVE-2026-33993 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-33993 affect?

CVE-2026-33993 affects locutus. Severity is critical (CVSS 9.8). 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 nota

How urgent is CVE-2026-33993?

Priority 56/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

PHP vulnerabilities

Related CVEs

CVE-2026-33994 CRITICAL 9.8 UPGRADE Locutus brings stdlibs of other programming languages to JavaScript for educational purposes

References

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