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CVE-2021-1624: Cisco IOS XE Software Rate Limiting Network Address Translation Denial of Service Vulnerability

• Severity: high (CVSS 8.6 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-09-23 · updated 2026-06-17
• Weakness: CWE-399

Description

A vulnerability in the Rate Limiting Network Address Translation (NAT) feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause high CPU utilization in the Cisco QuantumFlow Processor of an affected device, resulting in a denial of service (DoS) condition. This vulnerability is due to mishandling of the rate limiting feature within the QuantumFlow Processor. An attacker could exploit this vulnerability by sending large amounts of traffic that would be subject to NAT and rate limiting through an affected device. A successful exploit could allow the attacker to cause the QuantumFlow Processor utilization to reach 100 percent on the affected device, resulting in a DoS condition.

Affected products

• Cisco IOS XE: through 17.3.3

References

• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ratenat-pYVLA7wM
• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ratenat-pYVLA7wM

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