CVE-2026-73420: CWE-180: Incorrect Behavior Order: Validate Before Canonicalize in nextauthjs next-auth
CVE-2026-73420 is a critical vulnerability in NextAuth.js prior to versions 0.41.3 (@auth/core) and 4.24.15 (next-auth) and 5.0.0-beta.32. The issue arises because the default email address normalizer validates the address before applying Unicode normalization, allowing an attacker to exploit Unicode characters that canonicalize to ASCII '@' signs. This can cause magic link sign-in emails to be misrouted to attacker-controlled addresses, enabling unauthorized sign-in without victim interaction.
AI Analysis
Technical Summary
NextAuth.js versions before @auth/core 0.41.3 and next-auth 4.24.15 and 5.0.0-beta.32 use a defaultNormalizer for email and magic-link sign-in flows that validates email addresses before applying Unicode normalization. Unicode characters such as U+FF20 FULLWIDTH COMMERCIAL AT, which are not ASCII '@' but normalize to '@' under NFKC or NFKD, can bypass the single '@' check. Downstream mail libraries or delivery services that normalize addresses can then interpret the email as containing multiple '@' signs, causing the magic link to be sent to an attacker-controlled address. This allows an attacker who knows a victim's email to request a magic link and sign in as the victim without their interaction. The vulnerability is fixed in the specified versions.
Potential Impact
An attacker can exploit this vulnerability to receive passwordless sign-in magic links intended for a victim, enabling unauthorized access to the victim's account without their interaction. This compromises account security and authentication integrity in affected NextAuth.js implementations that use the default email normalizer and downstream normalization in email delivery.
Mitigation Recommendations
This issue is fixed in @auth/core version 0.41.3, next-auth version 4.24.15, and 5.0.0-beta.32. Users should upgrade to these or later versions to remediate the vulnerability. If a custom normalizeIdentifier is used instead of the built-in normalizer, verify that it correctly applies Unicode normalization before validation. Patch status is not explicitly stated beyond these fixed versions; check the vendor advisory for the latest remediation guidance.
CVE-2026-73420: CWE-180: Incorrect Behavior Order: Validate Before Canonicalize in nextauthjs next-auth
Description
CVE-2026-73420 is a critical vulnerability in NextAuth.js prior to versions 0.41.3 (@auth/core) and 4.24.15 (next-auth) and 5.0.0-beta.32. The issue arises because the default email address normalizer validates the address before applying Unicode normalization, allowing an attacker to exploit Unicode characters that canonicalize to ASCII '@' signs. This can cause magic link sign-in emails to be misrouted to attacker-controlled addresses, enabling unauthorized sign-in without victim interaction.
CVSS v4.0
Score 9.1critical
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
NextAuth.js versions before @auth/core 0.41.3 and next-auth 4.24.15 and 5.0.0-beta.32 use a defaultNormalizer for email and magic-link sign-in flows that validates email addresses before applying Unicode normalization. Unicode characters such as U+FF20 FULLWIDTH COMMERCIAL AT, which are not ASCII '@' but normalize to '@' under NFKC or NFKD, can bypass the single '@' check. Downstream mail libraries or delivery services that normalize addresses can then interpret the email as containing multiple '@' signs, causing the magic link to be sent to an attacker-controlled address. This allows an attacker who knows a victim's email to request a magic link and sign in as the victim without their interaction. The vulnerability is fixed in the specified versions.
Potential Impact
An attacker can exploit this vulnerability to receive passwordless sign-in magic links intended for a victim, enabling unauthorized access to the victim's account without their interaction. This compromises account security and authentication integrity in affected NextAuth.js implementations that use the default email normalizer and downstream normalization in email delivery.
Mitigation Recommendations
This issue is fixed in @auth/core version 0.41.3, next-auth version 4.24.15, and 5.0.0-beta.32. Users should upgrade to these or later versions to remediate the vulnerability. If a custom normalizeIdentifier is used instead of the built-in normalizer, verify that it correctly applies Unicode normalization before validation. Patch status is not explicitly stated beyond these fixed versions; check the vendor advisory for the latest remediation guidance.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-08-12T14:32:11.795Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a7e4130bf8831d539e05251
Added to database: 08/13/2026, 22:12:00 UTC
Last enriched: 08/13/2026, 22:26:21 UTC
Last updated: 08/14/2026, 02:32:26 UTC
Views: 31
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