Security readout for executives and security teams
Plain-English summary
This issue lets someone who already has administrator access to an affected Cisco Small Business RV Series router run operating system commands as root through the web management interface. The attacker must be authenticated with high privileges, which limits likelihood, but successful abuse could fully compromise the router.
Executive priority
Treat this as a targeted infrastructure hardening item, not an emergency based on the provided evidence. Prioritize internet-exposed or externally managed RV routers first because compromise of a router can affect traffic visibility, network trust boundaries, and downstream systems.
Technical view
CVE-2021-40120 is a CWE-20 command injection flaw in the web-based management interface of certain Cisco Small Business RV Series Router Firmware. Insufficient validation of user input can let an authenticated remote administrator execute arbitrary Linux commands with root privileges. CVSS 3.1 is 6.5: network attack vector, low complexity, high privileges required.
Likely exposure
Exposure is limited to organizations running affected Cisco Small Business RV Series routers where an attacker can reach the web management interface and authenticate with administrative privileges. Internet-exposed management interfaces and shared or weak administrator credentials increase practical risk.
Exploitation context
The provided bundle does not show CISA KEV listing or any cited evidence of active exploitation. Cisco describes exploitation as authenticated and remote, using malicious input in a specific web management field. No exploit status beyond the vendor description is supported here.
Researcher notes
The key limiting factor is PR:H: exploitation requires administrator privileges. Impact remains serious because successful exploitation runs commands as root on the underlying Linux OS. The source bundle does not provide specific affected model names, fixed versions, or exploitation telemetry, so validation should anchor on Cisco’s advisory.
Mitigation direction
- Check Cisco’s advisory for affected models, fixed releases, and any official workarounds.
- Apply Cisco-recommended firmware updates when available for the affected RV Series device.
- Restrict web management access to trusted administrative networks only.
- Review and reduce administrator accounts with access to router management.
- Disable remote management exposure where it is not operationally required.
Validation and detection
- Inventory Cisco Small Business RV Series routers and record firmware versions.
- Compare each device against the Cisco advisory’s affected and fixed version guidance.
- Confirm the web management interface is not exposed to untrusted networks.
- Review administrative account lists for unnecessary, shared, or stale accounts.
- Check router administrative logs for unexpected configuration changes or administrator activity.
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-20: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. 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 lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-40120 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
- 6.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N
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:H/UI:N/S:U/C:H/I:H/A:N1.25.2Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.5MediumVector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N
Source materials
- CVE List V5 sourceCVE List V5
- 20211103 Cisco Small Business RV Series Routers Command Injection 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.
Improper Input Validation
Improper Input Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.