CVE-2026-23478: Cal.com is open-source scheduling software

This month

CRITICAL 9.8REMOTEUPGRADE

CVE-2026-23478 is a critical-severity flaw (CVSS 9.8) affecting cal.com. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Critical severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 59%)
CISA exploited list	No
Weakness	CWE-602, CWE-639
Published	2026-01-13
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: cal

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-01-13 22:16 UTCPublished CVE record published
2026-06-17 10:21 UTCUpdated Record last modified

cal cal.com UPGRADE

Affected: >= 3.1.6 and < 6.0.7

Fixed in: 6.0.7

Safe to downgrade to: a release before 3.1.6

1. Check installed version

apt-cache policy cal.com || rpm -q cal.com || cal.com --version

2. UPGRADE to 6.0.7 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade cal.com

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade cal.com

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 3.1.6 (Debian / Ubuntu)

apt-cache madison cal.com sudo apt install cal.com=<VERSION_BEFORE_3.1.6> sudo apt-mark hold cal.com

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list cal.com sudo dnf downgrade cal.com-<VERSION_BEFORE_3.1.6> sudo dnf versionlock add cal.com

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-23478?

cal.com: upgrade to 6.0.7. Exact commands for each OS are on this page.

Is CVE-2026-23478 being exploited?

CVE-2026-23478 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-23478 affect?

CVE-2026-23478 affects cal.com. Severity is critical (CVSS 9.8). 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 add

How urgent is CVE-2026-23478?

Priority 49/100. Critical severity; Remotely exploitable, no login, no user action

Related CVEs

CVE-2025-66489 CRITICAL 9.8 UPGRADE Cal.com is open-source scheduling software

References

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