CVE-2026-73420: @auth Core

Critical severity, CVSS 9.1. EPSS: 0.7% chance of exploitation in the next 30 days.

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 defaultNormalizer used by the email and magic-link sign-in flow validates an address before applying Unicode normalization. An address can contain a Unicode character such as U+FF20 FULLWIDTH COMMERCIAL AT that is not ASCII at-sign but canonicalizes to an ASCII at-sign under NFKC or NFKD normalization. The address passes the normalizer's single-at-sign check, but a downstream sendVerificationRequest mail library or delivery service that normalizes the address can then see two at-sign separators and deliver the passwordless sign-in link to an attacker-controlled recipient. Applications are affected when the email provider uses the built-in normalizer rather than a custom normalizeIdentifier and the downstream sender applies Unicode normalization. An attacker who knows a victim's email address can request the misrouted magic link and sign in as the victim without victim interaction. This issue is fixed in @auth/core 0.41.3 and next-auth 4.24.15 and 5.0.0-beta.32.

Affected products

• @auth Core: from 0.1.0, before 0.41.3 (fixed in 0.41.3)
• Nextauthjs Next-Auth: before 4.24.15 (fixed in 4.24.15); from 5.0.0-beta.4, before 5.0.0-beta.32 (fixed in 5.0.0-beta.32)

Published 2026-08-13. Last modified 2026-09-18.