CVE-2023-20269
CVE-2023-20269 is a security flaw in Cisco Adaptive Security Appliance and Firepower Threat Defense, Cisco’s firewall. Attackers can get into Cisco Adaptive Security Appliance and Firepower Threat Defense 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 13 Sep 2023, and says ransomware gangs have used it.[1]
Cisco Adaptive Security Appliance and Firepower Threat Defense 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. Cisco has published a fix or advice.
Description
CISA calls it an unauthorized access in Cisco Adaptive Security Appliance and Firepower Threat Defense. In its words: “Cisco Adaptive Security Appliance and Firepower Threat Defense contain an unauthorized access vulnerability that could allow an unauthenticated, remote attacker to conduct a brute force attack in an attempt to identify valid username and password combinations or establish a clientless SSL VPN session with an unauthorized user.”[1]
The CVE record adds: “A vulnerability in the remote access VPN feature of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to conduct a brute force attack in an attempt to identify valid username and password combinations or an authenticated, remote attacker to establish a clientless SSL VPN session with an unauthorized user. This vulnerability is due to improper separation of authentication, authorization, and accounting (AAA) between the remote access VPN feature and the HTTPS management and site-to-site VPN features. An attacker could exploit this vulnerability by specifying a default connection profile/tunnel group while conducting a brute force attack or while establishing a clientless SSL VPN session using valid credentials. A successful exploit could allow the attacker to achieve…”[2]
The underlying weakness is authentication bypass (CWE-288), in MITRE’s list of common software weaknesses.
It scores 9.1 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 doesn’t list version ranges for it; Cisco’s advisory has them[3]. CISA names the product as Cisco Adaptive Security Appliance and Firepower Threat Defense.
Most families won’t have Cisco Adaptive Security Appliance and Firepower Threat Defense; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 13 Sep 2023, 7 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 4 Oct 2023 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 27%. That’s in the top 2% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
Cisco has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions for group-lock and vpn-simultaneous-logins or discontinue use of the product for unsupported devices.”[1]
- Check whether you use it.Cisco Adaptive Security Appliance and Firepower Threat Defense 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, or not in use. CISA gave US government agencies until 4 Oct 2023 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 9.1.[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 27%.[4] |
See also
Other Cisco flaws
- CVE-2026-76418, Cisco Secure Firewall ASA Software and Cisco Secure FTD Software: unchecked return value to NULL pointer dereference ·
- CVE-2026-76519, Cisco Secure Email Gateway: relative path traversal ·
- CVE-2026-76504, Cisco Catalyst SD-WAN Manager: hex encoding ·
- CVE-2026-76460, Cisco Identity Services Engine: incorrect use of privileged APIs ·
- CVE-2026-76461, Cisco Secure Email Gateway: SQL injection ·
Other authentication bypass flaws
- CVE-2026-19490, Citrix NetScaler: authentication bypass using an alternate path or channel ·
- CVE-2026-18556, N-able N-central: authentication bypass using an alternate path or channel ·
- CVE-2026-18577, N-able N-central: authentication bypass using an alternate path or channel ·
- CVE-2026-1603, Ivanti Endpoint Manager (EPM): authentication bypass ·
- CVE-2026-24858, Fortinet products: authentication bypass using an alternate path or channel ·
Added the same day
- CVE-2023-4863, Chrome and other Chromium browsers: heap-based buffer overflow ·
- CVE-2023-35674, Android Framework: privilege escalation ·
Every Cisco flaw on CISA’s list · Everything added in September 2023
References
- ^ Cybersecurity and Infrastructure Security Agency. “Cisco Adaptive Security Appliance and Firepower Threat Defense Unauthorized Access Vulnerability”. Known Exploited Vulnerabilities Catalog, added 13 Sep 2023.
- ^ National Institute of Standards and Technology. “CVE-2023-20269 Detail”. National Vulnerability Database, published 6 Sep 2023.
- ^ Cisco. Advisories and fixes: sec.cloudapps.cisco.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.266, percentile 98.0, 31 Oct 2026.
- CVE Program. “CVE-2023-20269”. 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.