Security readout for executives and security teams
Plain-English summary
CVE-2021-1624 is a denial-of-service flaw in Cisco IOS XE devices using Rate Limiting NAT. Remote unauthenticated traffic that is processed by NAT and rate limiting can drive the QuantumFlow Processor CPU to 100%, disrupting availability of the affected device.
Executive priority
Treat this as a high-priority availability risk for affected Cisco IOS XE routing infrastructure. It does not indicate data theft, but a successful attack can disrupt network service on critical paths.
Technical view
The issue is in Cisco IOS XE Software's Rate Limiting NAT feature. Cisco describes mishandling inside the QuantumFlow Processor when affected devices process traffic subject to NAT and rate limiting. CVSS 3.1 is 8.6, with network attack vector, low complexity, no privileges, no user interaction, and high availability impact.
Likely exposure
Exposure is most likely where Cisco IOS XE devices process traffic through NAT with rate limiting enabled. Internet-facing, perimeter, or high-throughput routing paths are higher business-risk because remote unauthenticated traffic can reach the vulnerable processing path.
Exploitation context
The source bundle describes remote unauthenticated DoS potential but does not cite active exploitation. The CVE is not marked as CISA KEV in the provided data. No public exploit details are included in the supplied sources.
Researcher notes
Evidence is limited to the CVE record and Cisco advisory metadata in the bundle. The vulnerable condition is tied to NAT plus rate limiting in the QuantumFlow Processor. Confirm precise affected versions and remediations directly from Cisco's advisory.
Mitigation direction
- Review Cisco's advisory for affected releases and fixed software guidance.
- Inventory Cisco IOS XE devices using NAT and rate limiting.
- Prioritize remediation for perimeter and business-critical routing devices.
- Monitor QuantumFlow Processor utilization for sustained unexplained saturation.
- Apply vendor-recommended updates or mitigations where Cisco identifies them.
Validation and detection
- Confirm whether each Cisco IOS XE device uses Rate Limiting NAT.
- Compare installed IOS XE versions against Cisco's advisory.
- Review device telemetry for QFP CPU reaching or approaching 100%.
- Check recent availability incidents on NAT/rate-limited paths.
- Validate monitoring alerts for processor saturation and service degradation.
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-399: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-1624 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 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/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:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H3.94Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.6HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- 20210922 Cisco IOS XE Software Rate Limiting Network Address Translation 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.