# CVE-2026-73420: Auth.js email normalizer homoglyph @ bypass in passwordless sign-in

Source: https://junglewise.ai/threats/cve-2026-73420-auth-js-email-normalizer-homoglyph-bypass-in-passwordless-sign-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-13. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-73420 · Severity: medium · CVSS 4 · Published 2026-08-13

Auth.js is a popular authentication library used to manage user login flows, including passwordless email sign-in. A flaw in its email validation allows attackers to use Unicode characters that look like @ symbols to bypass email address checks. An attacker can exploit this to intercept passwordless login links meant for a victim's email and use them to take over the victim's account without any interaction from the victim.

Technologies: [@auth/core (npm)](https://junglewise.ai/threats/technologies/auth-core), [next-auth (npm)](https://junglewise.ai/threats/technologies/next-auth). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-73420 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-73420 being exploited in the wild.

**How severe is CVE-2026-73420?** Medium severity, with a CVSS score of 4, published 13 August 2026.

**Which products and versions are affected?** @auth/core (npm) SEMVER:introduced=0.1.0,fixed=0.41.3; next-auth (npm) SEMVER:introduced=4.10.3,fixed=4.24.15.

**Is there a fix for CVE-2026-73420?** Yes. @auth/core (npm): upgrade to 0.41.3 or later; next-auth (npm): upgrade to 4.24.15 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-73420 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-73420?** Check whether you run @auth/core (npm) or next-auth (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- @auth/core (npm): upgrade to 0.41.3 or later

  ```sh
  npm install @auth/core@0.41.3
  ```

- next-auth (npm): upgrade to 4.24.15 or later

  ```sh
  npm install next-auth@4.24.15
  ```


## Technical details

The vulnerability is a validation-before-canonicalization flaw (CWE-180) in the email normalizer used by the passwordless sign-in provider. The normalizer validates email addresses for exactly one ASCII @ character before applying Unicode NFKC normalization. An attacker can craft an email address containing a homoglyph character (e.g., U+FF20 FULLWIDTH COMMERCIAL AT) that passes the single-@ check but normalizes to a real @ symbol when processed by downstream mail libraries. This causes the passwordless link to be delivered to a different, attacker-controlled recipient address. The attack requires no user interaction and is triggered when the attacker initiates the sign-in flow. Patches are available: @auth/core 0.41.3+, next-auth 4.24.15+, and next-auth 5.0.0-beta.32+.

## Affected products

- Auth.js @auth/core 0.1.0 to 0.41.2
- Auth.js next-auth 4.10.3 to 4.24.14, 5.0.0-beta.1 to 5.0.0-beta.31

## Identifiers

- CVE-2026-73420
- GHSA-7rqj-j65f-68wh

## Timeline

- 2026-07-23: disclosed: Published as GHSA-7rqj-j65f-68wh
- 2026-07-23: patched: @auth/core 0.41.3, next-auth 4.24.15, and 5.0.0-beta.32 released

## References

- [https://github.com/nextauthjs/next-auth/security/advisories/GHSA-7rqj-j65f-68wh](https://github.com/nextauthjs/next-auth/security/advisories/GHSA-7rqj-j65f-68wh)
- [https://github.com/nextauthjs/next-auth/commit/19d2feb24359fa8c79418907fc68d9ec8152ca94](https://github.com/nextauthjs/next-auth/commit/19d2feb24359fa8c79418907fc68d9ec8152ca94)

## Related threats

- [Auth.js authentication check bypass on configuration error](https://junglewise.ai/threats/cve-2026-73421-auth-js-authentication-check-bypass-on-configuration-error)
- [Auth.js OAuth provider-confusion in state/nonce/PKCE cookies](https://junglewise.ai/threats/cve-2026-73419-auth-js-oauth-provider-confusion-in-state-nonce-pkce-cookies)
- [NextAuth.js provides authentication for Next.js. Prior to @auth/core 0.41.3 and next-auth 4.24.15 and 5.0.0-beta.32, the exported getToken()](https://junglewise.ai/threats/cve-2026-73418-auth-js-gettoken-exception-on-malformed-bearer-headers)
- [NextAuth.js email misdelivery via nodemailer address parser bug](https://junglewise.ai/threats/nextauth-js-email-misdelivery-via-nodemailer-address-parser-bug-6824743e)
- [NextAuth.js authentication bypass via mock user creation](https://junglewise.ai/threats/cve-2023-48309-nextauth-js-authentication-bypass-via-mock-user-creation)