CVE-2020-2021
CVE-2020-2021 is a security flaw in Palo Alto Networks PAN-OS, the operating system on Palo Alto Networks’ firewalls. Attackers can get into Palo Alto Networks PAN-OS without a valid password. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 25 Mar 2022, and says ransomware gangs have used it.[1]
Palo Alto Networks PAN-OS is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fixed in version 8.1.15, 9.0.9 and 9.1.3 of PAN-OS.
Description
CISA calls it an authentication bypass in Palo Alto Networks PAN-OS. In its words: “Palo Alto Networks PAN-OS contains a vulnerability in SAML which allows an attacker to bypass authentication.”[1]
The CVE record adds: “When Security Assertion Markup Language (SAML) authentication is enabled and the 'Validate Identity Provider Certificate' option is disabled (unchecked), improper verification of signatures in PAN-OS SAML authentication enables an unauthenticated network-based attacker to access protected resources. The attacker must have network access to the vulnerable server to exploit this vulnerability. This issue affects PAN-OS 9.1 versions earlier than PAN-OS 9.1.3; PAN-OS 9.0 versions earlier than PAN-OS 9.0.9; PAN-OS 8.1 versions earlier than PAN-OS 8.1.15, and all versions of PAN-OS 8.0 (EOL). This issue does not affect PAN-OS 7.1. This issue cannot be exploited if SAML is not used for authentication. This issue cannot be exploited if the 'Validate Identity Provider Certificate' option is enabled (checked) in the SAML Identity Provider Server Profile. Resources that can be…”[2]
The underlying weakness is CWE-347, in MITRE’s list of common software weaknesses.
It scores 10.0 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]
| Product | Fixed in |
|---|---|
| PAN-OS | 8.1.15 |
| PAN-OS | 9.0.9 |
| PAN-OS | 9.1.3 |
Most families won’t have Palo Alto Networks PAN-OS; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 25 Mar 2022, 634 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 15 Apr 2022 to fix it.[1] CISA says ransomware gangs have used it.
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 4%. That’s in the top 9% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
Palo Alto Networks has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Check whether you use it.Palo Alto Networks PAN-OS is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed (fixed in version 8.1.15, 9.0.9 and 9.1.3 of PAN-OS), or not in use. CISA gave US government agencies until 15 Apr 2022 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 10.0.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks, noting that ransomware gangs have used it.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 4%.[4] |
See also
Other Palo Alto Networks PAN-OS flaws
- CVE-2026-0322: code injection ·
- CVE-2026-0257: authentication bypass ·
- CVE-2026-0300: out-of-bounds write ·
- CVE-2025-0111: file read ·
- CVE-2025-0108: authentication bypass ·
- CVE-2024-3393: malicious DNS packet ·
Other Palo Alto Networks flaws
- CVE-2024-9465, Palo Alto Networks Expedition: SQL injection ·
- CVE-2024-9463, Palo Alto Networks Expedition: OS command injection ·
- CVE-2024-5910, Palo Alto Networks Expedition: missing authentication ·
Similar flaws
- CVE-2026-5430, WSO2 products: path traversal ·
- CVE-2026-48558, SimpleHelp: authentication bypass ·
- CVE-2025-59718, Fortinet products: improper verification of cryptographic signature ·
- CVE-2022-20703, Cisco Small Business RV160, RV260, RV340, and RV345 Series Routers: small business RV series routers stack-based buffer overflow ·
- CVE-2020-1464, Microsoft Windows: spoofing ·
Added the same day
- CVE-2022-26318, WatchGuard Firebox and XTM Appliances: arbitrary code execution ·
- CVE-2022-26143, Mitel MiCollab, MiVoice Business Express: access control ·
- CVE-2022-21999, Microsoft Windows: print spooler privilege escalation ·
- CVE-2021-42237, Sitecore XP: remote command execution ·
- CVE-2021-22941, Citrix ShareFile: improper access control ·
Every Palo Alto Networks flaw on CISA’s list · Everything added in March 2022
References
- ^ Cybersecurity and Infrastructure Security Agency. “Palo Alto Networks PAN-OS Authentication Bypass Vulnerability”. Known Exploited Vulnerabilities Catalog, added 25 Mar 2022.
- ^ National Institute of Standards and Technology. “CVE-2020-2021 Detail”. National Vulnerability Database, published 29 Jun 2020.
- ^ Palo Alto Networks. Advisories and fixes: security.paloaltonetworks.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.044, percentile 91.3, 31 Oct 2026.
- CVE Program. “CVE-2020-2021”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.