Security readout for executives and security teams
Plain-English summary
This flaw can let an unauthenticated remote attacker crash certain Cisco cBR-8 broadband routers by abusing DHCPv4 handling on WAN-facing interfaces. The business impact is service disruption: an affected router may reload, interrupting broadband routing availability.
Executive priority
Treat as high priority for broadband or service-provider networks using Cisco cBR-8. The issue affects availability, not data theft, but router reloads can interrupt customer-facing network service.
Technical view
CVE-2020-3509 is insufficient error handling in the DHCPv4 message parser of Cisco IOS XE Software for Cisco cBR-8 Converged Broadband Routers. A crafted DHCPv4 message sent to or through a WAN interface can crash the supervisor and trigger device reload. CVSS is 8.6 high, with availability impact only.
Likely exposure
Exposure is likely limited to environments running Cisco cBR-8 Converged Broadband Routers with Cisco IOS XE Software. The bundle does not identify specific affected versions. Cisco treats 10 Gbps, 100 Gbps Ethernet, and related port-channel interfaces as WAN interfaces for this issue.
Exploitation context
The CVSS vector indicates network reachability, low complexity, no privileges, and no user interaction. The provided sources do not show CISA KEV listing or active exploitation evidence, so active exploitation should not be assumed.
Researcher notes
The source bundle establishes product, impact, attack vector, CVSS, CWE-388, and WAN-interface scope. It does not include exact affected versions, fixed releases, workarounds, or exploit-in-the-wild evidence. Use Cisco’s advisory for authoritative version and remediation details.
Mitigation direction
- Identify all Cisco cBR-8 routers running IOS XE Software.
- Review the Cisco advisory for affected and fixed software guidance.
- Prioritize remediation on devices with untrusted DHCPv4 exposure on WAN interfaces.
- Restrict unnecessary DHCPv4 traffic to or through WAN interfaces where operationally safe.
- Monitor affected routers for unexpected supervisor crashes or reloads.
Validation and detection
- Confirm whether deployed devices are Cisco cBR-8 Converged Broadband Routers.
- Map WAN interfaces, including 10G, 100G, and related port channels.
- Compare installed IOS XE versions against Cisco’s advisory guidance.
- Review operational logs for DHCP-related faults, supervisor crashes, or reloads.
- Verify external or untrusted paths cannot send DHCPv4 traffic through exposed WAN interfaces.
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-388: 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 lookupCVE-2020-3509 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
- 8.6 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/AV:N/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:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H3.94Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
8.6HighVector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- 20200924 Cisco IOS XE Software for Cisco cBR-8 Converged Broadband Routers DHCP 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.
7PK - Errors
7PK - Errors represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.