CVE-2025-66489
Auth Bypass in Cal.Com ≤ 5.9.8
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:N/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-2025-66489 is a critical-severity Incorrect Implementation of Authentication Algorithm (CWE-303) vulnerability in Cal Cal.Com. Its CVSS base score is 9.9 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique External Remote Services (T1133); ranked in the top 45% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-15 (Development Process, Standards, and Tools) — 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-2025-66489 is a critical authentication bypass vulnerability in Cal.com, an open-source scheduling software. In versions prior to 5.9.8, a flaw in the login credentials provider enables attackers to skip password verification when a TOTP code is supplied, stemming from faulty conditional logic in the authentication flow. The vulnerability 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 maps to CWE-303 (Incorrect Implementation of Authentication Algorithm).
Any unauthenticated attacker with network access can exploit this issue remotely with low complexity and no user interaction required. Exploitation allows bypassing password checks during login attempts that include a valid TOTP code, resulting in unauthorized access to affected user accounts and high-impact compromise of confidentiality, integrity, and availability.
The vulnerability is remediated in Cal.com version 5.9.8. Additional details on the fix and affected configurations are available in the GitHub security advisory at https://github.com/calcom/cal.com/security/advisories/GHSA-9r3w-4j8q-pw98.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-201128
Vulnerability Data
Cal.com is open-source scheduling software. Prior to 5.9.8, A flaw in the login credentials provider allows an attacker to bypass password verification when a TOTP code is provided, potentially gaining unauthorized access to user accounts. This issue exists due to…
more
problematic conditional logic in the authentication flow. This vulnerability is fixed in 5.9.8.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation at post-design stages directly uncovers incorrect implementations of required authentication algorithms.
Requiring documented development processes, standards, and tools reduces the chance that an established authentication algorithm is coded incorrectly.
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.
Secure SDLC practices directly require correct implementation of authentication algorithms.
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 authentication control directly requires correct implementation of authentication algorithms.
Security testing can detect flawed authentication implementations but does not prevent them by itself.
Cryptography control addresses proper use of authentication algorithms but is broader than authentication alone.
Secure development lifecycle includes verification steps that can catch incorrect authentication implementations.
Application security requirements can specify correct authentication algorithm use but do not guarantee correct implementation.
Secure coding practices reduce the likelihood of incorrect authentication algorithm implementation.