# CVE-2026-23478: Cal.com has an Authentication Bypass via Unvalidated Email in Custom JWT Callback

> Attackers can bypass authentication and take over any user account by exploiting an unvalidated email parameter in the custom JWT callback.

- **Severity:** Critical 10.0 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 13 Jan 2026
- **Updated:** 14 Jan 2026
- **Also known as:** GHSA-7hg4-x4pr-3hrg

## What is CVE-2026-23478?

CVE-2026-23478 is a critical authentication bypass vulnerability in calcom cal.com, published on 13 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Cal.com is open-source scheduling software. From 3.1.6 to before 6.0.7, there is a vulnerability in a custom NextAuth JWT callback that allows attackers to gain full authenticated access to any user's account by supplying a target email address via session.update(). This vulnerability is fixed in 6.0.7.

Weakness: CWE-639 (Authorization Bypass Through User-Controlled Key), CWE-602 (Client-Side Enforcement of Server-Side Security)

## Which versions are affected by CVE-2026-23478?

It affects 1 product.


Products: Cal Cal.com.

## How do I fix CVE-2026-23478?

No fix has been published for CVE-2026-23478 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-23478 being exploited?

There is no known exploitation of CVE-2026-23478 in the wild and no public exploit code.

## Other vulnerabilities in calcom cal.com

- [CVE-2025-66489](https://insights.sbomify.com/CVE-2025-66489/): Cal.com Authentication Bypass via bad TOTP + password checks (critical 9.9)
- [CVE-2023-1647](https://insights.sbomify.com/CVE-2023-1647/): Improper Access Control in calcom/cal.com (high 8.8)
- [CVE-2023-37919](https://insights.sbomify.com/CVE-2023-37919/): Cal.com not expiring old sessions after enabling 2FA (medium 6.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-23478 and fix it if it is affected.

What it is: CVE-2026-23478 is a critical authentication bypass vulnerability in calcom cal.com, published on 13 Jan 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-2026-23478 in the wild and no public exploit code.

Affected product: calcom cal.com. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-23478/ (Markdown: https://insights.sbomify.com/CVE-2026-23478/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23478
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23478
- OSV: https://osv.dev/vulnerability/CVE-2026-23478

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23478/
Summaries are generated and may contain mistakes; the official description above is the record.