GHSA-xv97-c62v-4587

### Impact `next-auth` users who are using the `EmailProvider` either in versions before `4.10.3` or `3.29.10` are affected. If an attacker could forge a request that sent a comma-separated list of emails (eg.: `[email protected],[email protected]`) to the sign-in endpoint, NextAuth.js would send emails to both the attacker and the victim's e-mail addresses. The attacker could then login as a newly created user with the email being `[email protected],[email protected]`. This means that basic authorization like `email.endsWith("@victim.com")` in the `signIn` callback would fail to communicate a threat to the developer and would let the attacker bypass authorization, even with an `@attacker.com` address. ### Patches We patched this vulnerability in `v4.10.3` and `v3.29.10` by normalizing the email value that is sent to the sign-in endpoint before accessing it anywhere else. We also added a `normalizeIdentifier` callback on the `EmailProvider` configuration, where you can further tweak your requirements for what your system considers a valid e-mail address. (E.g.: strict RFC2821 compliance) To upgrade, run one of the following: ```sh npm i next-auth@latest ``` ```sh yarn add next-auth@latest ``` ```sh pnpm add next-auth@latest ``` (This will update to the latest v4 version, but you can change `latest` to `3` if you want to stay on v3. This is not recommended. v3 is unmaintained.) ### Workarounds If for some reason you cannot upgrade, you can normalize the incoming request like the following, using Advanced Initialization: ```ts // pages/api/auth/[...nextauth].ts function normalize(identifier) { // Get the first two elements only, // separated by `@` from user input. let [local, domain] = identifier.toLowerCase().trim().split("@") // The part before "@" can contain a "," // but we remove it on the domain part domain = domain.split(",")[0] return `${local}@${domain}` } export default async function handler(req, res) { if (req.body.email) req.body.email = normalize(req.body.email) return await NextAuth(req, res, {/* your options */ }) } ``` ### References - EmailProvider: https://next-auth.js.org/providers/email - Normalize the email address: https://next-auth.js.org/providers/email#normalizing-the-email-address - Email syntax: https://en.wikipedia.org/wiki/Email_address#Local-part - `signIn` callback: https://next-auth.js.org/configuration/callbacks#sign-in-callback - Advanced Initialization: https://next-auth.js.org/configuration/initialization#advanced-initialization - `nodemailer` address: https://nodemailer.com/message/addresses ### For more information If you have any concerns, we request responsible disclosure, outlined here: https://next-auth.js.org/security#reporting-a-vulnerability ### Timeline The issue was reported 26th of July, a response was sent out in less than 1 hour and after identifying the issue a patch was published within 5 working days. ### Acknowledgments We would like to thank [Socket](https://socket.dev) for disclosing this vulnerability in a responsible manner and following up until it got published.