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

> Attackers can hijack user accounts by exploiting Unicode normalization flaws in email validation to misroute magic-link sign-in emails.

- **Severity:** Critical 9.1 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 13 Aug 2026
- **Updated:** 14 Aug 2026
- **Also known as:** CLEANSTART-2026-PJ45513, CLEANSTART-2026-UY65626, ECHO-2dd4-1209-8fa6, GHSA-7rqj-j65f-68wh, MINI-9rhj-8fjf-x394, MINI-hqcv-vx43-gc7f, MINI-p7xj-prjj-q33p

## What is CVE-2026-73420?

CVE-2026-73420 is a critical authentication bypass vulnerability in @auth core, published on 13 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-180 (Incorrect Behavior Order: Validate Before Canonicalize)

## Which versions are affected by CVE-2026-73420?

6 open source packages ship an affected version, including @auth/core and next-auth.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@auth/core` | npm | From 0.1.0 | 0.41.3 |
| `@auth/core` | npm | From 0.1.0 | 0.41.3 |
| `next-auth` | npm | From 4.10.3 | 4.24.15 |
| `next-auth` | npm | From 4.10.3 | 4.24.15 |
| `next-auth` | npm | From 5.0.0-beta.1 | 5.0.0-beta.32 |
| `next-auth` | npm | From 5.0.0-beta.1 | 5.0.0-beta.32 |

## How do I fix CVE-2026-73420?

Upgrade @auth/core to 0.41.3 or later.

## Is CVE-2026-73420 being exploited?

There is no known exploitation of CVE-2026-73420 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-73420 and fix it if it is affected.

What it is: CVE-2026-73420 is a critical authentication bypass vulnerability in @auth core, published on 13 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-73420 in the wild and no public exploit code.

Affected packages and fixed versions:
- @auth/core (npm): affected from 0.1.0; fixed in 0.41.3
- @auth/core (npm): affected from 0.1.0; fixed in 0.41.3
- next-auth (npm): affected from 4.10.3; fixed in 4.24.15
- next-auth (npm): affected from 4.10.3; fixed in 4.24.15
- next-auth (npm): affected from 5.0.0-beta.1; fixed in 5.0.0-beta.32
- next-auth (npm): affected from 5.0.0-beta.1; fixed in 5.0.0-beta.32

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-73420/ (Markdown: https://insights.sbomify.com/CVE-2026-73420/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-73420
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-73420
- OSV: https://osv.dev/vulnerability/CVE-2026-73420

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-73420/
Summaries are generated and may contain mistakes; the official description above is the record.