CVE-2026-23478
Access Control in Cal.Com 3.1.6 – 6.0.7
Raw vector
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:XSummary
CVE-2026-23478 is a critical-severity Client-Side Enforcement of Server-Side Security (CWE-602) vulnerability in Cal Cal.Com. Its CVSS base score is 10.0 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 34th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-24 (Access Control Decisions) and AC-25 (Reference Monitor) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-23478 is a critical authentication bypass vulnerability in Cal.com, an open-source scheduling software. It affects versions from 3.1.6 up to but not including 6.0.7, stemming from a flaw in a custom NextAuth JWT callback. Attackers can supply a target email address via the session.update() function to gain full authenticated access to any user's account. The issue carries a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) and is linked to CWE-602 (Client-Side Enforcement of Server-Side Security) and CWE-639 (Authorization Bypass Through User-Controlled Key).
Unauthenticated attackers can exploit this vulnerability remotely with low attack complexity and no user interaction required. By manipulating the session update mechanism, they achieve complete impersonation of any target user, enabling unauthorized access to sensitive scheduling data, account modifications, and potential further compromise within the application.
The official Cal.com security advisory (https://github.com/calcom/cal.com/security/advisories/GHSA-7hg4-x4pr-3hrg) documents the vulnerability, confirming it is fixed in version 6.0.7. Administrators should immediately upgrade to 6.0.7 or later to mitigate the risk.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-2413
Vulnerability Data
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().…
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This vulnerability is fixed in 6.0.7.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V10.7.1V2.2.2V8.3.1V10.4.1
Mitigating Controls (NIST 800-53 r5) AI
Requires a tamper-proof, always-invoked reference monitor that cannot be bypassed by client-side logic.
Enforces all access decisions on the server according to policy rather than trusting client-supplied enforcement.
Requiring explicit access-control decisions on each request blocks unauthorized key-driven access.
Enforces information-flow rules at the server boundary instead of delegating them to the client.
Least-privilege restrictions limit the scope of data reachable even if a key check is bypassed.
Monitors and controls all external and key internal interfaces so that server-side policy cannot be off-loaded to clients.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Enforcing authorization policy and least privilege directly blocks user-controlled key tampering that bypasses access checks.
Logical access controls prevent unauthorized data access that results from missing authorization checks on object references.
Secure SDLC practices directly prevent design flaws that place server security enforcement on the client.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Secure architecture principles discourage client-side trust but do not directly address this weakness.
Security testing can detect client-side enforcement but is not the primary mitigation.
Information access restriction is undermined when the client is trusted to enforce it.
Access control policy directly requires enforcement of authorization rules that prevent unauthorized access via manipulated keys.
Managing access rights includes ensuring users can only access their own records and not bypass authorization by altering identifiers.
Privileged access rights control restricts what data each user may access, mitigating direct object reference attacks.