Security readout for executives and security teams
Plain-English summary
CVE-2021-1378 is a denial-of-service flaw in Cisco StarOS SSH handling. A remote unauthenticated attacker could disrupt an affected device so it stops processing traffic. The business impact is service availability, not data theft or system takeover, based on the supplied sources.
Executive priority
Handle as a moderate availability risk. Escalate priority if affected ASR 5000 devices support revenue-generating or customer-facing traffic, especially when SSH is exposed beyond tightly controlled administration paths.
Technical view
The vulnerability is a StarOS SSH service logic error triggered under specific traffic conditions. Cisco ASR 5000 Series Software is listed as affected. CVSS 3.1 is 5.3, network-accessible, low complexity, no privileges, no user interaction, with low availability impact only.
Likely exposure
Exposure is most relevant where Cisco ASR 5000 Series Software runs StarOS and SSH is reachable from untrusted networks. Actual exposure depends on deployed release, SSH reachability, and management-plane filtering, which are not detailed in the bundle.
Exploitation context
The sources describe remote unauthenticated exploitation by crafted packets causing DoS. The bundle does not provide exploit code, public exploitation evidence, or KEV listing; KEV is false. Treat exploitation status as unconfirmed rather than active.
Researcher notes
Evidence is limited to the CVE description and Cisco advisory reference. The affected version details are not included in the supplied bundle, so validation should center on Cisco's advisory and local asset inventory rather than assumptions about releases.
Mitigation direction
- Review Cisco's advisory for affected releases and vendor-approved fixes.
- Restrict SSH access to trusted management networks only.
- Prioritize remediation for internet-reachable or carrier-critical StarOS devices.
- Monitor affected devices for traffic-processing disruption and SSH anomalies.
- Apply Cisco-recommended updates or workarounds where applicable.
Validation and detection
- Inventory Cisco ASR 5000 Series Software and StarOS deployments.
- Compare deployed versions against Cisco's advisory guidance.
- Verify SSH is blocked from untrusted networks.
- Check monitoring for unexplained DoS or traffic-processing stoppage.
- Confirm availability remains stable after remediation changes.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
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CWE-400: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-1378 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.3 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L3.91.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.3MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source materials
- CVE List V5 sourceCVE List V5
- 20210217 Cisco StarOS Denial of Service VulnerabilityCVE reference · vendor-advisory, x_refsource_CISCO
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Uncontrolled Resource Consumption
Uncontrolled Resource Consumption represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.