CVE-2020-2021
Palo Alto Networks PAN-OS Authentication Bypass Vulnerability
Description
CVE-2020-2021 is a critical SAML authentication bypass vulnerability in Palo Alto Networks PAN-OS. When SAML authentication is enabled and the 'Validate Identity Provider Certificate' option is disabled, an unauthenticated network attacker can bypass authentication and access protected resources, including the PAN-OS management interface. This vulnerability has a CVSS score of 10.0 (CRITICAL) and was added to the CISA Known Exploited Vulnerabilities catalog on March 25, 2022. With an EPSS score of 97.1% (99.9th percentile), exploitation is near-certain, making immediate remediation essential for any organization using affected PAN-OS configurations.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:HOpen in CalculatorCWEs
Affected Products
| Vendor | Product | Version |
|---|---|---|
| paloaltonetworks | pan-os | >= 8.0.0, <= 8.0.20; >= 8.1.0, < 8.1.15; >= 9.0.0, < 9.0.9; >= 9.1.0, < 9.1.3 |
Multiple CVSS Assessments
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
References
- https://security.paloaltonetworks.com/CVE-2020-2021(Mitigation, Vendor Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-2021(US Government Resource)
Weakness Type
CWE-347: Improper Verification of Cryptographic Signature
CVE-2020-2021 is classified under CWE-347, which involves improper verification of cryptographic signatures. In this case, PAN-OS fails to properly validate the identity provider certificate during SAML authentication when the 'Validate Identity Provider Certificate' option is disabled, allowing attackers to forge SAML assertions and bypass authentication entirely.
Learn more: CWE-347 — Improper Verification of Cryptographic Signature
Impact Analysis
CVE-2020-2021 carries a maximum CVSS 3.1 score of 10.0 (CRITICAL) with the vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H. The vulnerability is remotely exploitable by an unauthenticated attacker with no user interaction required, and it affects the changed scope, meaning the compromised component can impact resources beyond its security authority. Successful exploitation grants full access to the PAN-OS management interface or any SAML-protected resource, enabling complete confidentiality, integrity, and availability compromise. The attack complexity is low — the only prerequisite is that SAML authentication is enabled and certificate validation is disabled. Given the EPSS score of 97.1%, organizations with this configuration face near-certain exploitation risk.
Exploit Maturity
CVE-2020-2021 has been confirmed as actively exploited in the wild by CISA, which added it to the Known Exploited Vulnerabilities catalog. The vulnerability's simplicity — requiring only that SAML be enabled with certificate validation disabled — makes it trivially exploitable without specialized tooling. With an EPSS score of 97.1% (99.9th percentile), this vulnerability is among the most likely to be exploited, and organizations should assume that any exposed, misconfigured PAN-OS device is a target.
Remediation
- Enable 'Validate Identity Provider Certificate': Immediately enable the 'Validate Identity Provider Certificate' option in the SAML Identity Provider Server Profile on all PAN-OS devices to prevent forged SAML assertion attacks.
- Upgrade PAN-OS to a patched version: Apply the latest PAN-OS security updates from Palo Alto Networks that address CVE-2020-2021, following the vendor's published security advisory.
- Restrict management interface access: Ensure the PAN-OS management interface is not exposed to the internet and is only accessible from trusted internal networks or via VPN.
- Review SAML authentication logs: Audit authentication logs for suspicious SAML-based logins that may indicate prior exploitation, particularly any access from unexpected IP addresses or at unusual times.
- Implement multi-factor authentication: Deploy additional authentication layers beyond SAML to reduce the risk of single-point authentication bypass.
Technical Details
CVE-2020-2021 exploits a flaw in the SAML authentication implementation of Palo Alto Networks PAN-OS. When SAML-based single sign-on (SSO) is configured and the 'Validate Identity Provider Certificate' option is set to disabled (or unchecked), the PAN-OS device does not properly verify the cryptographic signature on SAML assertions received from the identity provider. This allows an unauthenticated attacker to craft or replay SAML assertions that the device accepts as legitimate, granting access to any SAML-protected resource including the management web interface, GlobalProtect VPN, and Captive Portal. The root cause is a failure in signature validation (CWE-347), where the absence of certificate validation means any well-formed SAML response is trusted regardless of its origin.
Frequently Asked Questions
Is CVE-2020-2021 being actively exploited?
Yes. CISA has confirmed active exploitation of CVE-2020-2021 and added it to the Known Exploited Vulnerabilities catalog on March 25, 2022. With an EPSS score of 97.1%, exploitation is near-certain for exposed and misconfigured systems.
What products are affected by CVE-2020-2021?
CVE-2020-2021 affects Palo Alto Networks PAN-OS when SAML authentication is enabled and the 'Validate Identity Provider Certificate' option is disabled. This impacts PAN-OS management interfaces, GlobalProtect, and Captive Portal configurations using SAML SSO.
How do I fix CVE-2020-2021?
Enable the 'Validate Identity Provider Certificate' option in the SAML Identity Provider Server Profile configuration and upgrade PAN-OS to the latest patched version. Restrict management interface access to trusted networks only.
How severe is CVE-2020-2021?
CVE-2020-2021 is rated CRITICAL with the maximum CVSS score of 10.0. It allows unauthenticated attackers to completely bypass authentication and gain full administrative access to affected Palo Alto Networks devices, representing one of the most severe firewall vulnerabilities disclosed.
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