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CVE-2021-1378: Cisco StarOS Denial of Service Vulnerability

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-02-17 · updated 2026-06-17
• Weakness: CWE-400

Description

A vulnerability in the SSH service of the Cisco StarOS operating system could allow an unauthenticated, remote attacker to cause an affected device to stop processing traffic, resulting in a denial of service (DoS) condition. The vulnerability is due to a logic error that may occur under specific traffic conditions. An attacker could exploit this vulnerability by sending a series of crafted packets to an affected device. A successful exploit could allow the attacker to prevent the targeted service from receiving any traffic, which would lead to a DoS condition on the affected device.

Affected products

• Cisco StarOS: from 21.9.0 through 21.19.10

References

• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-StarOS-DoS-RLLvGFJj
• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-StarOS-DoS-RLLvGFJj

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