How severe is CVE-2026-73420?

No CVSS score has been assigned to CVE-2026-73420 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-73420?

CVE-2026-73420 affects the following packages: @auth/core (npm), next-auth (npm), next-auth (npm). Ecosystems affected: npm.

How do I fix CVE-2026-73420?

Update @auth/core to 0.41.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-73420 is resolved across your whole dependency graph.

How do I detect CVE-2026-73420 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @auth/core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-73420 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-73420 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-73420 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-73420?

CVE-2026-73420 has an EPSS (Exploit Prediction Scoring System) score of 0.7%, placing it in the 52th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-73420?

CVE-2026-73420 is classified as CWE-180 (CWE-180). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-73420 published, and has it been updated?

CVE-2026-73420 was published on August 13, 2026 and was last updated on September 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

CVE-2026-73420 — @auth/core

Fix: nextauthjs/next-auth@19d2feb

CVE-2026-73420 is a CWE-180 vulnerability in @auth/core. A fix is available for @auth/core — see the affected versions and patch details below.

NextAuth.js: Email normalizer validates the address before Unicode normalization, allowing a homoglyph @ bypass

Also known asGHSA-7rqj-j65f-68wh

Published

Aug 13, 2026

Updated

Sep 20, 2026

Affected

3 pkgs

Patched

3 / 3

Exploits

None indexed

Exploitation data as of Sep 27, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
A successful exploit gives an attacker total control of the affected component, not partial access.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-73420.

EPSS Exploitation Probability

via FIRST.org ↗

0.7%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs52th percentile — riskier than 52% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

3 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

158other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

@auth/corenpm

5.0Mdownloads / week

next-authnpm

6.8Mdownloads / week

Description

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, < 4.24.14, or @auth/core >= 0.1.0, < 0.41.3.
You have the email / magic-link (passwordless) provider enabled.
You rely on the built-in default identifier normalizer (you have not supplied your own normalizeIdentifier).
Your sendVerificationRequest implementation uses a mail library or delivery service that applies Unicode normalization to recipient addresses (most internationalized-email/SMTPUTF8-capable senders do).

You are not affected if you do not use the email provider, or if your normalizer/mailer rejects or canonicalizes non-ASCII addresses before they are validated.

Impact

Account takeover: an attacker who knows a victim's email address can request a magic link that is delivered to an attacker-controlled mailbox, then use it to sign in as the victim.
No victim interaction is required to misroute the link; the attacker initiates the flow.

Patched version

The fix applies Unicode (NFKC) normalization before the address is validated, so homoglyph separators are collapsed and rejected up front. Upgrade to the first release containing this fix (pending; this advisory will be updated with the exact patched version before publication). No application code changes are required after upgrading.

Workarounds

If you cannot upgrade immediately:

Supply a custom normalizeIdentifier on the email provider that calls identifier.normalize("NFKC") (and lower-cases/trims) before any validation, and rejects addresses that do not contain exactly one @ after normalization.
Or reject any address whose local part or domain contains non-ASCII characters, if your user base does not require internationalized email addresses.

Credit

Reported by @kakashi-kx. Thank you for the responsible disclosure.

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`@auth/core`	≥ 0.1.0&&< 0.41.3	0.41.3`npm install @auth/core@0.41.3`
📦npm	`next-auth`	≥ 4.10.3&&< 4.24.15	4.24.15`npm install next-auth@4.24.15`
📦npm	`next-auth`	≥ 5.0.0-beta.1&&< 5.0.0-beta.32	5.0.0-beta.32`npm install next-auth@5.0.0-beta.32`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @auth/core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @auth/core to 0.41.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-73420 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

## 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

O3 Security · Impact-Aware SCA

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