Security readout for executives and security teams
Plain-English summary
This flaw affects Cisco Small Business RV Series routers through LLDP, a local network discovery protocol. A nearby attacker on the same Layer 2 network could crash the router, leak memory, or potentially execute arbitrary code. It is not described as remotely exploitable from the internet by the provided sources.
Executive priority
Treat this as high priority for branch, SMB, or remote-office networks using Cisco RV routers. The attack is local-network adjacent, but router compromise or outages can disrupt connectivity and security controls. Prioritize inventory, vendor guidance review, and segmentation of untrusted LAN access.
Technical view
CVE-2021-1309 is a CWE-119 memory-safety issue in Cisco RV Series router LLDP handling. The CVSS 3.1 score is 7.4 high, with adjacent-network attack vector, low complexity, no privileges, no user interaction, changed scope, and high availability impact.
Likely exposure
Exposure is most likely where affected Cisco Small Business RV Series routers share a broadcast domain with untrusted or compromised devices. Internet exposure alone is not the key condition; Layer 2 adjacency is required according to the Cisco/CVE description.
Exploitation context
The bundle does not cite CISA KEV listing or active exploitation. Exploitation requires same-broadcast-domain access. The public description says successful exploitation could lead to arbitrary code execution, memory leak, or router reload causing denial of service.
Researcher notes
Evidence is limited to the CVE bundle and Cisco advisory reference. Do not assume internet exploitability, affected model list, fixed versions, or exploit availability beyond the cited source. The key constraint is LLDP Layer 2 adjacency in the same broadcast domain.
Mitigation direction
- Review Cisco's advisory for affected models, fixed firmware, and supported workarounds.
- Apply vendor-recommended firmware updates where applicable.
- Restrict untrusted devices from the router's Layer 2 broadcast domain.
- Limit physical and switch-port access to networks containing affected routers.
- Monitor affected networks for unexpected router reloads or memory instability.
- If LLDP is unnecessary, verify Cisco-supported options to disable or restrict it.
Validation and detection
- Inventory Cisco Small Business RV Series routers and firmware versions.
- Compare deployed devices against Cisco's CVE-2021-1309 advisory scope.
- Map broadcast domains that include affected routers.
- Identify untrusted hosts with Layer 2 adjacency to those routers.
- Review router logs for unexplained reloads, memory issues, or LLDP-related faults.
- Confirm remediation status after applying Cisco guidance.
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-119: 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-2021-1309 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
- 7.4 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/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:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H2.84Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.4HighVector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- 20210407 Cisco Small Business RV Series Routers Link Layer Discovery Protocol 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.
Improper Restriction of Operations within the Bounds of a Memory Buffer
Improper Restriction of Operations within the Bounds of a Memory Buffer represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.