Security readout for executives and security teams
Plain-English summary
This flaw can let someone on the same local network segment crash an affected Cisco ASR 9000 line card. The business risk is service disruption on carrier or enterprise aggregation routers, not data theft. Exposure depends on whether vulnerable IOS XR software and affected ASR 9000 line cards are deployed.
Executive priority
Treat as high priority for networks where ASR 9000 routers carry critical traffic or face shared Layer 2 environments. The main concern is outage or degraded routing capacity, so remediation should align with maintenance windows but not be deferred indefinitely.
Technical view
CVE-2021-34713 is an adjacent-network denial-of-service issue in Cisco IOS XR Layer 2 punt handling for ASR 9000 Series Aggregation Services Routers. Incorrect handling of specific Ethernet frames can trigger a spin loop, make network processors unresponsive, and reboot the affected line card.
Likely exposure
Most relevant to organizations operating Cisco ASR 9000 Series routers with IOS XR in aggregation or service-provider environments. Internet remote attack is not indicated; the attacker must be adjacent to the Layer 2 segment connected to affected line cards.
Exploitation context
The provided bundle does not show CISA KEV listing or other evidence of active exploitation. The attack requires unauthenticated adjacent access and low complexity, so compromised or untrusted devices on connected Ethernet segments could raise operational risk.
Researcher notes
The available sources identify the affected product family and attack precondition but do not provide exploit details in the bundle. Avoid assuming broader IOS XR exposure beyond Cisco ASR 9000 Series routers unless Cisco's advisory confirms it.
Mitigation direction
- Check Cisco's advisory for affected releases and fixed software guidance.
- Inventory ASR 9000 routers and IOS XR versions in production networks.
- Prioritize vendor-recommended updates for exposed aggregation routers.
- Restrict untrusted Layer 2 access to attached segments where feasible.
- Monitor for unexpected line card reboots or processor unresponsiveness.
Validation and detection
- Confirm whether Cisco ASR 9000 Series routers are deployed.
- Map installed IOS XR versions against Cisco's advisory.
- Identify line cards connected to shared or untrusted Ethernet segments.
- Review logs for line card reloads around suspicious Layer 2 activity.
- Document compensating controls until vendor guidance is applied.
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-399: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-34713 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
- 20210908 Cisco IOS XR Software for ASR 9000 Series Routers 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.
Resource Management Errors
Resource Management Errors represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.