CVE-2026-73420: Auth.js: Email normalizer validates the address before Unicode normalization, allowing a homoglyph @ bypass

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.7%, percentile 53: FIRST’s model estimates a 0.7% chance of exploitation activity in the next 30 days, higher than 53% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes @auth/core (npm) >= 0.1.0, < 0.41.3, fixed in 0.41.3; next-auth (npm) >= 4.10.3, < 4.24.15, fixed in 4.24.15; next-auth (npm) >= 5.0.0-beta.1, <= 5.0.0-beta.31, fixed in 5.0.0-beta.32. Check your lockfile, including transitive dependencies.

What it is

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.

From the GitHub advisory

Summary

The default email-address normalizer used by the email/magic-link sign-in flow validates the address before applying Unicode normalization. An address can contain a Unicode character that is not an ASCII @ (U+0040) but canonicalizes to one under NFKC/NFKD normalization (the normalization commonly applied by mail libraries and services for internationalized email). Such an address passes the normalizer's single-@ check, but a downstream mail library that normalizes the string then sees two @ separators and may deliver the passwordless sign-in link to a different recipient than intended. This is an instance of validating before canonicalizing.

Am I affected?

You may be affected if all of the following hold:

- You use next-auth >= 4.0.0, = 0.1.0,

Weakness type: CWE-180.

Product: @auth/core (npm) · Assigned by: GitHub_M · Published: 2026-08-13

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: present (depends on deployment conditions)
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.73% probability of exploitation activity in the next 30 days; percentile 53.

Timeline

• 2026-07-23 — GitHub-reviewed advisory GHSA-7rqj-j65f-68wh published (critical)
• 2026-08-13 — CVE record published by GitHub_M
• 2026-08-14 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-7rqj-j65f-68wh github.com
2. CVE.org record CVE-2026-73420 cve.org
3. NVD entry CVE-2026-73420 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com
5. github.com github.com
6. github.com github.com

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