CVE-2019-1687: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software TCP Proxy Denial of Service Vulnerability

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 2.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2019-05-03 · updated 2026-08-11
Weakness: CWE-20

Description

A vulnerability in the TCP proxy functionality for Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to restart unexpectedly, resulting in a denial of service (DoS) condition. The vulnerability is due to an error in TCP-based packet inspection, which could cause the TCP packet to have an invalid Layer 2 (L2)-formatted header. An attacker could exploit this vulnerability by sending a crafted TCP packet sequence to the targeted device. A successful exploit could allow the attacker to cause a DoS condition.

Affected products

Cisco ASA Software: before 9.4.4.34; from 9.5 before 9.6.4.25; from 9.7 before 9.8.4; from 9.9 before 9.9.2.50; from 9.10 before 9.10.1.17 — fixed in 9.10.1.17, 9.4.4.34, 9.6.4.25, 9.8.4, 9.9.2.50
Cisco Firepower Threat Defense Software: from 6.0.0 before 6.2.3.12; from 6.3.0 before 6.3.0.3 — fixed in 6.2.3.12, 6.3.0.3

How to fix

Upgrade to a fixed version: Cisco ASA Software 9.10.1.17, 9.4.4.34, 9.6.4.25, 9.8.4; Cisco Firepower Threat Defense Software 6.2.3.12, 6.3.0.3. Check the vendor advisory for mitigations.

References

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