CVE-2016-6366
CVE-2016-6366 is a security flaw in Cisco Adaptive Security Appliance (ASA), Cisco’s firewall. Someone who already has a way in can use Cisco Adaptive Security Appliance (ASA) to run their own code. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 24 May 2022.[1]
Cisco Adaptive Security Appliance (ASA) 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.
Description
CISA calls it an SNMP buffer overflow in Cisco Adaptive Security Appliance (ASA). In its words: “A buffer overflow vulnerability in the Simple Network Management Protocol (SNMP) code of Cisco ASA software could allow an attacker to cause a reload of the affected system or to remotely execute code.”[1]
The CVE record adds: “Buffer overflow in Cisco Adaptive Security Appliance (ASA) Software through 9.4.2.3 on ASA 5500, ASA 5500-X, ASA Services Module, ASA 1000V, ASAv, Firepower 9300 ASA Security Module, PIX, and FWSM devices allows remote authenticated users to execute arbitrary code via crafted IPv4 SNMP packets, aka Bug ID CSCva92151 or EXTRABACON.”[2]
The underlying weakness is memory buffer error (CWE-119), in MITRE’s list of common software weaknesses.
It scores 8.8 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it. CISA names the product as Cisco Adaptive Security Appliance (ASA).
Most families won’t have Cisco Adaptive Security Appliance (ASA); it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 24 May 2022, 2,105 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 14 Jun 2022 to fix it.[1]
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 88%. That’s in the top 1% of the flaws it scores.[3]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
CISA’s required action: “Apply updates per vendor instructions.”[1]
- Check whether you use it.Cisco Adaptive Security Appliance (ASA) 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 14 Jun 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 8.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[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 88%.[3] |
See also
Other Cisco Adaptive Security Appliance (ASA) flaws
- CVE-2014-2120: cross-site scripting (XSS) ·
- CVE-2016-6367: CLI remote code execution ·
- CVE-2018-0296: denial-of-service ·
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 memory buffer error flaws
- CVE-2026-88779, Citrix NetScaler: improper restriction of operations within the bounds of a memory buffer ·
- CVE-2026-88772, Citrix NetScaler: improper restriction of operations within the bounds of a memory buffer ·
- CVE-2026-88771, Citrix NetScaler: improper input validation ·
- CVE-2026-8452, Citrix NetScaler ADC and NetScaler Gateway: improper restriction of operations within the bounds of a memory buffer ·
- CVE-2009-3459, Adobe Acrobat and Reader: heap-based buffer overflow ·
Added the same day
- CVE-2018-8611, Microsoft Windows: kernel privilege escalation ·
- CVE-2018-19953, QNAP Network Attached Storage (NAS): NAS file station cross-site scripting ·
- CVE-2018-19949, QNAP Network Attached Storage (NAS): NAS file station command injection ·
- CVE-2018-19943, QNAP Network Attached Storage (NAS): NAS file station cross-site scripting ·
- CVE-2017-8543, Microsoft Windows: search remote code execution ·
Every Cisco flaw on CISA’s list · Everything added in May 2022
References
- ^ Cybersecurity and Infrastructure Security Agency. “Cisco Adaptive Security Appliance (ASA) SNMP Buffer Overflow Vulnerability”. Known Exploited Vulnerabilities Catalog, added 24 May 2022.
- ^ National Institute of Standards and Technology. “CVE-2016-6366 Detail”. National Vulnerability Database, published 18 Aug 2016.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.876, percentile 99.8, 31 Oct 2026.
- CVE Program. “CVE-2016-6366”. 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.