CVE-2022-20821
CVE-2022-20821 is a security flaw in Cisco IOS XR, the operating system on Cisco’s routers and switches. Attackers are using a flaw in Cisco IOS XR. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 23 May 2022.[1]
Cisco IOS XR 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 open port in Cisco IOS XR. In its words: “Cisco IOS XR software health check opens TCP port 6379 by default on activation. An attacker can connect to the Redis instance on the open port and allow access to the Redis instance that is running within the NOSi container.”[1]
The CVE record adds: “A vulnerability in the health check RPM of Cisco IOS XR Software could allow an unauthenticated, remote attacker to access the Redis instance that is running within the NOSi container. This vulnerability exists because the health check RPM opens TCP port 6379 by default upon activation. An attacker could exploit this vulnerability by connecting to the Redis instance on the open port. A successful exploit could allow the attacker to write to the Redis in-memory database, write arbitrary files to the container filesystem, and retrieve information about the Redis database. Given the configuration of the sandboxed container that the Redis instance runs in, a remote attacker would be unable to execute remote code or abuse the integrity of the Cisco IOS XR Software host system.”[2]
The underlying weakness is CWE-923, in MITRE’s list of common software weaknesses.
It scores 6.5 out of 10 on the Common Vulnerability Scoring System, which rates it medium, 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 IOS XR.
Most families won’t have Cisco IOS XR; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 23 May 2022. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 13 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 11%. That’s in the top 4% 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
Cisco has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Check whether you use it.Cisco IOS XR 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 13 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 |
|---|---|
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| The flaw is made public in the National Vulnerability Database, with a severity score of 6.5.[2] | |
| 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 11%.[4] |
See also
Other Cisco IOS XR flaws
- CVE-2010-3035: border gateway protocol (BGP) denial-of-service ·
- CVE-2009-2055: border gateway protocol (BGP) denial-of-service ·
- CVE-2020-3569: software DVMRP memory exhaustion ·
- CVE-2020-3566: software DVMRP memory exhaustion ·
- CVE-2020-3118: software discovery protocol format string ·
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 ·
Added the same day
- CVE-2021-30883, Apple devices: memory corruption ·
- CVE-2021-1048, Android Kernel: use-after-free ·
- CVE-2021-0920, Android Kernel: race condition ·
- CVE-2020-1027, Microsoft Windows: kernel privilege escalation ·
- CVE-2020-0638, Microsoft Update Notification Manager: privilege escalation ·
Every Cisco flaw on CISA’s list · Everything added in May 2022
References
- ^ Cybersecurity and Infrastructure Security Agency. “Cisco IOS XR Open Port Vulnerability”. Known Exploited Vulnerabilities Catalog, added 23 May 2022.
- ^ National Institute of Standards and Technology. “CVE-2022-20821 Detail”. National Vulnerability Database, published 26 May 2022.
- ^ Cisco. Advisories and fixes: tools.cisco.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.115, percentile 96.0, 31 Oct 2026.
- CVE Program. “CVE-2022-20821”. 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.