CVE-2021-34781
No exploitation reported by the sources we read.
- Published2021-10-27
- WeaknessCWE-119 · CWE-755
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
A vulnerability in the processing of SSH connections for multi-instance deployments of Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on the affected device. This vulnerability is due to a lack of proper error handling when an SSH session fails to be established. An attacker could exploit this vulnerability by sending a high rate of crafted SSH connections to the instance. A successful exploit could allow the attacker to cause resource exhaustion, which causes a DoS condition on the affected device. The device must be manually reloaded to recover.
Timeline
dates in UTC- 2021-10-2719:15CVE publishedNVD
Observed activity
isMalicious corpus · updated 2026-10-23 18:48 UTCBlock these indicators
- Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-34781?format=txt
- CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-34781?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 |
|---|---|---|---|
| 6.3 | = 6.3.0 | no fix published | NVD |
| 6.4 | = 6.4.0 | no fix published | NVD |
| 6.4 | = 6.4.0.13 | no fix published | NVD |
| 6.5 | = 6.5.0 | no fix published | NVD |
| 6.6 | = 6.6.0 | no fix published | NVD |
| 6.7 | = 6.7.0.3 | no fix published | NVD |
| 6.7 | = 6.7.1 | no fix published | NVD |
| 7.0 | = 7.0.0 | no fix published | NVD |
| Branch | Affected | Fixed in | Source |
|---|---|---|---|
| 6.3 | = 6.3.0 | no fix published | NVD |
| 6.4 | = 6.4.0 | no fix published | NVD |
| 6.4 | = 6.4.0.13 | no fix published | NVD |
| 6.5 | = 6.5.0 | no fix published | NVD |
| 6.6 | = 6.6.0 | no fix published | NVD |
| 6.7 | = 6.7.0.3 | no fix published | NVD |
| 6.7 | = 6.7.1 | no fix published | NVD |
| 7.0 | = 7.0.0 | no fix published | NVD |
| Branch | Affected | Fixed in | Source |
|---|---|---|---|
| 7.0 | ≥ 7.0.0, < 7.0.1 | 7.0.1 | NVD |
| 6.7 | ≥ 6.7.0, < 6.7.0.3 | 6.7.0.3 | NVD |
| 6.x | ≥ 6.5.0, < 6.6.5 | 6.6.5 | NVD |
| 6.x | ≥ 6.3.0, < 6.4.0.13 | 6.4.0.13 | NVD |
as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.
Fix
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
Technical details
- CVSS v3 Vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Published
- 2021-10-27
- Last Modified
- 2026-08-11
- NVD status
- Modified
Frequently asked questions
What is CVE-2021-34781?
Is CVE-2021-34781 actively exploited?
What is the CVSS score for CVE-2021-34781?
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