Security readout for executives and security teams
Plain-English summary
This flaw can let someone on an adjacent network segment crash and reload affected Cisco IOS or IOS XE devices that process ISDN Q.931 messages. The business impact is service interruption, not data theft, but affected network equipment could briefly drop connectivity or routing availability.
Executive priority
Treat this as a high-priority availability risk for networks still using affected Cisco IOS or IOS XE ISDN capabilities. It is less urgent for environments without ISDN/Q.931 exposure, but confirmed exposed devices should be remediated promptly.
Technical view
CVE-2020-3511 is an insufficient input validation issue in the ISDN subsystem when processing ISDN Q.931 messages. An unauthenticated adjacent attacker could send a malicious Q.931 message that crashes the process and reloads the device. CVSS v3.0 is 7.4 high, with high availability impact only.
Likely exposure
Exposure is most likely where Cisco IOS or IOS XE devices run affected software and have ISDN Q.931 processing reachable from an adjacent attacker. The provided sources do not list exact vulnerable versions or configurations in the bundle.
Exploitation context
The source bundle does not show CISA KEV listing or cited evidence of active exploitation. Exploitation requires adjacent network access, no credentials, low complexity, and no user interaction. Successful exploitation causes denial of service through device reload.
Researcher notes
The vulnerability maps to CWE-20 and is availability-only: no confidentiality or integrity impact is claimed. The key constraint is attack adjacency, so exposure validation should focus on device role, ISDN/Q.931 configuration, and reachable Layer 2 or telecom adjacency.
Mitigation direction
- Check Cisco advisory for affected releases and fixed software guidance.
- Upgrade affected Cisco IOS or IOS XE devices per Cisco guidance.
- Limit adjacency to ISDN/Q.931-capable interfaces to trusted networks.
- Monitor affected devices for unexpected reloads or ISDN subsystem crashes.
- Prioritize redundancy for devices carrying critical connectivity.
Validation and detection
- Inventory Cisco IOS and IOS XE devices with ISDN functionality enabled.
- Compare installed software versions against Cisco advisory applicability.
- Review device logs for reloads linked to ISDN or Q.931 processing.
- Confirm untrusted adjacent systems cannot reach ISDN signaling paths.
- Document affected, fixed, and not-applicable devices.
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-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 lookupCVE-2020-3511 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 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/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:3.0/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H2.84Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
7.4HighVector: CVSS:3.0/AV:A/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 and IOS XE Software ISDN Q.931 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.
Improper Input Validation
Improper Input Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.