CVE-2026-122131 PUBLISHED

Joi 17.13.6 before 17.13.9 and 18.2.5 before 18.3.1 Prototype Replacement via proto Language Key

Assigner: VulnCheck
Reserved: 04.11.2026 Published: 04.11.2026 Updated: 04.11.2026

Joi 17.13.6 before 17.13.9 and 18.2.5 before 18.3.1 contains a prototype pollution vulnerability in lib/messages.js compile() and merge() that fails to reject a proto language key. Attackers supplying untrusted message configuration via any().messages(), prefs, validate options or Joi.extend can replace the compiled messages prototype, altering or breaking validation error rendering and dependent logic.

CVSS Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
CVSS Score: 6.3

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	None	Confidentiality	None
Attack Complexity	High	Integrity	Low	Integrity	None
Attack Requirements	Present	Availability	None	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
CVSS Score: 3.7

Attack Vector	Network	Scope	Unchanged
Attack Complexity	High	Confidentiality Impact	None
Privileges Required	None	Integrity Impact	Low
User Interaction	None	Availability Impact	None

CVSS 3.1

Product Status

Vendor	hapijs
Product	joi
Versions	Default: unaffected affected from 17.13.6 to 17.13.9 (excl.) affected from 18.2.5 to 18.3.1 (excl.)

Credits

Zachariah Mithani (AploSec) finder
Marsup remediation developer

References

Problem Types

Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') CWE