CVE-2021-1220
No exploitation reported by the sources we read.
- Published2021-03-24
- WeaknessCWE-20
Am I affected?
Debian, Ubuntu or Red Hat sometimes backport a fix without changing the upstream version number: such a version reads « to verify », never « affected ».With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.
Description
Multiple vulnerabilities in the web UI of Cisco IOS XE Software could allow an authenticated, remote attacker with read-only privileges to cause the web UI software to become unresponsive and consume vty line instances, resulting in a denial of service (DoS) condition. These vulnerabilities are due to insufficient error handling in the web UI. An attacker could exploit these vulnerabilities by sending crafted HTTP packets to an affected device. A successful exploit could allow the attacker to cause the web UI software to become unresponsive and consume all available vty lines, preventing new session establishment and resulting in a DoS condition. Manual intervention would be required to regain web UI and vty session functionality. Note: These vulnerabilities do not affect the console connection.
Timeline
dates in UTC- 2021-03-2421:15CVE publishedNVD
Observed activity
isMalicious corpus · updated 2026-10-23 21:37 UTCBlock these indicators
- Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-1220?format=txt
- CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-1220?format=csv
- TAXII collection of exploited CVEs
- The EDL and CSV take an API key on the Pro plan.
Versions per branch
NVD| Branch | Affected | Fixed in | Source |
|---|---|---|---|
| 3.15 | = 3.15.1xbs | no fix published | NVD |
| 3.15 | = 3.15.2xbs | no fix published | NVD |
| 16.11 | = 16.11.1 | no fix published | NVD |
| 16.11 | = 16.11.1a | no fix published | NVD |
| 16.11 | = 16.11.1b | no fix published | NVD |
| 16.11 | = 16.11.1c | no fix published | NVD |
| 16.11 | = 16.11.1s | no fix published | NVD |
| 16.11 | = 16.11.2 | no fix published | NVD |
| 16.12 | = 16.12.1 | no fix published | NVD |
| 16.12 | = 16.12.1a | no fix published | NVD |
| 16.12 | = 16.12.1c | no fix published | NVD |
| 16.12 | = 16.12.1s | no fix published | NVD |
as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.
Distribution builds and vendor advisories
Packages from OSV.dev and products from the vendors' CSAF advisories.
version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.
Vendor advisories
ICSA-21-110-02_Rockwell Automation Stratix Switches
Stratix 5400: Versions 15.2(7)E3 and earlier · Stratix 5700: Versions 15.2(7)E3 and earlier · Stratix 5410: Versions 15.2(7)E3 and earlier · +2 more
Fix
- Vendor fix CISA ICSA-21-110-02 · 5 productsStratix 5800: Apply Version 17.04.01 or later. If possible, disable DECnet protocol completely or on select interfaces.
- Mitigation from the vendor CISA ICSA-21-110-02 · 5 productsRockwell Automation encourages users of the affected Stratix devices to update to an available firmware revision that addresses the associated risk.
- Mitigation from the vendor CISA ICSA-21-110-02 · 5 productsStratix 8300: Migrate to contemporary solution.
- Mitigation from the vendor CISA ICSA-21-110-02 · 5 productsAll versions, including Stratix 8000, Stratix 5700, Stratix 5410, Stratix 5400: Confirm the least-privilege user principle is followed, and user account access to is only granted with a minimum number of rights as needed.
- Mitigation from the vendor CISA ICSA-21-110-02 · 5 productsPlease see the Rockwell Automation security advisory for more detailed information.
- Mitigation from the vendor CISA ICSA-21-110-02 · 5 productsWhere a fix is not yet available, users who are unable to update are directed towards the risk mitigation strategies provided below, and are encouraged, when possible, to apply general security guidelines to employ multiple strategies simultaneously.
Advisories and patches
- tools.cisco.comVendor Advisory
Detection
- Nuclei template
- none so far ProjectDiscovery
- Exploit-DB
- no entry Exploit-DB
- Proof-of-concept repositories
- none listed PoC-in-GitHub
Sources
- CNACVSS 3.14.3read 2026-10-23
- NVDCVSS 3.14.3read 2026-10-23
- NVDCVSS 2.03.5read 2026-10-23
- CNAweakness (CWE)CWE-20read 2026-10-23
- FIRST EPSSEPSS score1.0 %2026-10-22
Technical details
- CVSS v3 Vector
- CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
- Published
- 2021-03-24
- Last Modified
- 2026-06-17
- NVD status
- Modified
Frequently asked questions
What is CVE-2021-1220?
Is CVE-2021-1220 actively exploited?
What is the CVSS score for CVE-2021-1220?
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Related vulnerabilities
Same product first, then the same vendor advisory and the same publication week.