Security readout for executives and security teams
Plain-English summary
CVE-2021-1539 affects Cisco ASR 5000 Series Software, also known as StarOS. A logged-in remote user could bypass authorization checks and run some CLI commands they should not be allowed to run. Business risk is highest where ASR 5000 devices support carrier or critical network services.
Executive priority
Treat as high priority for telecom, carrier, or critical network environments using ASR 5000. Prioritize inventory, vendor-advisory review, access restriction, and software remediation planning.
Technical view
The issue is an authorization bypass in Cisco ASR 5000 Series Software, mapped to CWE-863. CVSS 3.1 is 8.1 with network attack vector, low complexity, low privileges required, no user interaction, high confidentiality impact, and high availability impact. The source bundle does not provide exact affected versions.
Likely exposure
Exposure is limited to organizations running Cisco ASR 5000 Series Software. The attacker needs valid access to the device or management plane, so risk depends heavily on admin account control, management-plane reachability, and StarOS version status.
Exploitation context
The provided sources do not show CISA KEV listing or confirmed active exploitation. The vulnerability is still serious because a low-privileged authenticated user could exceed intended CLI permissions on network infrastructure.
Researcher notes
Evidence supports an authenticated remote authorization bypass with confidentiality and availability impact. The bundle does not include exact vulnerable versions, fixed releases, workaround details, or the specific CLI command subset, so avoid over-scoping without the Cisco advisory details.
Mitigation direction
- Identify all Cisco ASR 5000 Series Software deployments.
- Review Cisco’s advisory for affected releases, fixed software, and mitigations.
- Restrict ASR 5000 management access to trusted administration networks.
- Review privileged and low-privileged accounts for least-privilege alignment.
- Monitor administrative activity for unexpected CLI use.
Validation and detection
- Confirm whether any ASR 5000 devices run StarOS in your environment.
- Compare installed software releases against Cisco advisory guidance.
- Review AAA and role-based CLI authorization settings.
- Audit logs for unexpected commands by authenticated users.
- Verify management interfaces are not broadly reachable.
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
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-863: Authorization and privilege behavior lookup
Authorization weaknesses can support privilege escalation and valid-account review, depending on exploit path. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupPrivilege behavior lookup
The CVE wording references privilege impact, so privilege escalation and authorization behavior review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-1539 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
- High
- CVSS
- 8.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
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:L/UI:N/S:U/C:H/I:N/A:H2.85.2Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.1HighVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- 20210602 Cisco ASR 5000 Series Software Authorization Bypass VulnerabilitiesCVE 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.
Incorrect Authorization
Incorrect Authorization represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.