Security readout for executives and security teams
Plain-English summary
This flaw affects Cisco Small Business RV Series routers’ LLDP handling. A device on the same local network segment could crash or reload a router, leak system memory, or potentially execute code. The main business risk is local network disruption at sites using affected RV routers.
Executive priority
Treat this as high priority for affected small-site or branch routing infrastructure, especially where untrusted users can connect locally. It is less urgent than an internet-exploitable router flaw, but a successful attack could disrupt connectivity and operations at impacted locations.
Technical view
CVE-2021-1251 covers multiple LLDP implementation vulnerabilities in Cisco Small Business RV Series Router Firmware. The CVSS 3.1 score is 7.4, with adjacent attack vector, low complexity, no privileges, and no user interaction. Cisco describes unauthenticated Layer 2-adjacent impact including arbitrary code execution, memory disclosure, memory leak, and reload-based DoS.
Likely exposure
Exposure is limited to environments running affected Cisco Small Business RV Series routers where an attacker can reach the same Layer 2 broadcast domain. Remote internet exposure is not indicated by the provided sources. Version and model specificity are incomplete in the bundle and should be confirmed against Cisco’s advisory.
Exploitation context
The source bundle does not show CISA KEV listing or other cited evidence of active exploitation. Exploitation requires local Layer 2 adjacency because LLDP is not routed across networks. Risk is higher on shared, poorly segmented, or physically accessible networks.
Researcher notes
The public bundle confirms CWE-119, adjacent-vector exploitation, and Cisco RV Series firmware impact, but lacks affected version granularity and named fixes. Avoid assuming internet exploitability. Focus validation on LLDP exposure, Layer 2 adjacency, firmware inventory, and Cisco advisory matching.
Mitigation direction
- Review Cisco’s advisory for affected models, fixed firmware, and supported workarounds.
- Prioritize remediation for branch, retail, and shared-network sites using RV Series routers.
- Limit untrusted devices on the same broadcast domain as affected routers.
- Restrict physical and switch-port access where these routers are deployed.
- Monitor vendor guidance because fixes are not detailed in the supplied bundle.
Validation and detection
- Inventory Cisco Small Business RV Series routers and record firmware versions.
- Check whether LLDP is enabled or exposed on router-facing switch ports.
- Map which user or guest networks share a broadcast domain with each router.
- Review router logs for unexplained reloads, instability, or memory-related failures.
- Compare discovered models and firmware against Cisco’s advisory.
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-2021-1251 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.