CVE-2021-34698: Cisco Web Security Appliance Proxy Service Denial of Service Vulnerability

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-10-06 · updated 2026-06-17
Weakness: CWE-401

Description

A vulnerability in the proxy service of Cisco AsyncOS for Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to exhaust system memory and cause a denial of service (DoS) condition on an affected device. This vulnerability is due to improper memory management in the proxy service of an affected device. An attacker could exploit this vulnerability by establishing a large number of HTTPS connections to the affected device. A successful exploit could allow the attacker to cause the system to stop processing new connections, which could result in a DoS condition. Note: Manual intervention may be required to recover from this situation.

Affected products

Cisco Asyncos: from 12.0 before 12.0.3-005; from 12.5 before 12.5.2-007; from 14.0 before 14.0.1-014 — fixed in 12.0.3-005, 12.5.2-007, 14.0.1-014

How to fix

Upgrade to a fixed version: Cisco Asyncos 12.0.3-005, 12.5.2-007, 14.0.1-014. Check the vendor advisory for mitigations.

References

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