CVE-2026-33863: Convict has prototype pollution via load(), loadFile(), and schema initialization

Should you act?

Critical, preconditions apply

Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog. That can change quickly after a public write-up; re-check if you are affected.
• Needs local access needed. Lower urgency for most teams unless an attacker could already run code on the machine.
• Only applies if your dependency tree includes convict (npm) <= 6.2.4, fixed in 6.2.5. Check your lockfile, including transitive dependencies.

What it is

From the GitHub advisory

Impact Two unguarded prototype pollution paths exist, not covered by previous fixes:

1. config.load() / config.loadFile() — overlay() recursively merges config data without checking for forbidden keys. Input containing proto or constructor.prototype (e.g. from a JSON file) causes the recursion to reach Object.prototype and write attacker-controlled values onto it. 2. Schema initialization — passing a schema with constructor.prototype. keys to convict({...}) causes default-value propagation to write directly to Object.prototype at startup.

Depending on how polluted properties are consumed, impact ranges from unexpected behavior to authentication bypass or RCE.

Workarounds Do not pass untrusted data to load(), loadFile(), or convict().

Resources Prior advisory: GHSA-44fc-8fm5-q62h Related issue: https://github.com/mozilla/node-convict/issues/423

Weakness type: CWE-1321.

Product: convict (npm) · Published: 2026-03-26

Affected and fixed versions

Severity scores

• Attack vector: local access needed
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).

Timeline

• 2026-03-26 — GitHub-reviewed advisory GHSA-hf2r-9gf9-rwch published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-hf2r-9gf9-rwch github.com
2. CVE.org record CVE-2026-33863 cve.org
3. NVD entry CVE-2026-33863 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

Critical npm advisories · Today’s Security Digest