joi (npm package joi, hapi.js) versions =17.2.0 17.13.7 and =18.0.0 18.2.6 are vulnerable to regular expression denial of service in the Joi.string().isoDate() validation rule. One of the regular expressions the rule applies to the input is unanchored, so a valid ISO date followed by a long run of fractional-second digits causes the regex engine to restart its search from every position in the string, yielding time proportional to the square of the input length (about 1.4 s for 64 KB of digits and about 22 s for 256 KB). A remote attacker who can supply a string to an isoDate validation can stall the application with a single request. Fixed in 17.13.7 and 18.2.6; as a workaround, cap the length of the string before it reaches joi.

Impact An application that passes attacker-controlled data into joi's custom message configuration (messages(), message(), prefs({ messages }), Joi.extend({ messages }) or rule({ message })) lets the attacker write properties onto Object.prototype, where every object in the process then inherits them. A key named proto was treated as a language name, and the code reused the object it found at that key, which resolves to the prototype rather than to a new own property; a key named constructor did the same to the Object function's statics. A consuming application that gates on the mere presence of a property (if (user.isAdmin)) can be made to take the wrong branch for every object it inspects.

This is not reachable from data that joi validates. Custom messages are schema-construction configuration, normally written by the application developer. Exploitation therefore requires an application that feeds untrusted input straight into schema construction.

Patches Upgrade to version 18.2.5 or 17.13.6.

Workarounds Do not pass untrusted input into messages(), message(), prefs({ messages }), Joi.extend({ messages }) or rule({ message }). Or validate that they don't contain any proto or constructor property.