Raw vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:NCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2024-20355 is a medium-severity Missing Authorization (CWE-862) vulnerability in Cisco Adaptive Security Appliance Software. Its CVSS base score is 5.0 (Medium).
Operationally, ranked at the 25th 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.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2024-18070
Vulnerability Data
A vulnerability in the implementation of SAML 2.0 single sign-on (SSO) for remote access VPN services in Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an authenticated, remote attacker to successfully establish a…
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VPN session on an affected device. This vulnerability is due to improper separation of authorization domains when using SAML authentication. An attacker could exploit this vulnerability by using valid credentials to successfully authenticate using their designated connection profile (tunnel group), intercepting the SAML SSO token that is sent back from the Cisco ASA device, and then submitting the same SAML SSO token to a different tunnel group for authentication. A successful exploit could allow the attacker to establish a remote access VPN session using a connection profile that they are not authorized to use and connect to secured networks behind the affected device that they are not authorized to access. For successful exploitation, the attacker must have valid remote access VPN user credentials.
- CWE(s)
Related Threats
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
AC-3 directly requires enforcement of authorization decisions on every access request, structurally eliminating missing authorization checks.
AC-24 mandates that access control decisions are applied to each request, preventing bypass of authorization logic.
AC-25 requires a tamperproof, always-invoked reference monitor that ensures authorization checks cannot be omitted.
AC-6 reduces the set of actions reachable without proper authorization, limiting blast radius of missing checks.
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.
Requiring formal authorization of every access request before rights are granted ensures that checks for required permissions are performed, preventing missing authorization checks from being introduced.
A.5.18's provisioning, review, revocation and activation steps (incl. owner approval, SoD, timely removal on role/termination change) directly stop exploitation of missing authorization checks by ensuring no actor receives or retains rights to resources they should not access; the bounded remainder is that it cannot stop missing-authorization defects inside the enforcement mechanism itself once rights have been granted (e.g. flawed code that ignores the rights table).
By requiring competent outsiders to verify that every function enforces the need-to-know principle, the control lowers the likelihood that missing authorization checks persist undetected.
A.5.8 integrates risk assessment, requirements elicitation and governance into the project lifecycle so that authorization needs can be identified and specified; it does not itself perform or enforce authorization checks, so the missing-authorization weakness can still be present and exploitable.
Security checkpoints and explicit authorization requirements in the design phase ensure that every sensitive function is paired with an access-control check, reducing missing-authorization defects.
A.8.27 mandates security-by-design principles (least privilege, default deny, security architecture integration, zero-trust never-trust/always-verify, dynamic access control) plus design reviews that directly specify and enforce authorization checks before access; this stops most missing-authorization cases from being exploitable, with a bounded remainder in non-architectural or legacy components where the principles were documented but not fully applied.
Hardening callouts derived
DISA STIG baselines are authored against specific weaknesses. Where this CVE cites a broad weakness class, the mapping is not asserted at that abstraction (owner ruling, 2026-09-25: grade only at Base and below), so no rule is shown here rather than a rule shown against the wrong grain.
- No fine-grained STIG row for CWE-862, a class-level weakness, and none of its children carries one either.