---
id: CVE-2018-15399
title: >-
  A vulnerability in the TCP syslog module of Cisco Adaptive Security Appliance
  (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow
  an unauthenticated, remote attacker to exhaust the 1550-byte buffers on an
  affecte…
summary: >-
  A vulnerability in the TCP syslog module of Cisco Adaptive Security Appliance
  (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow
  an unauthenticated, remote attacker to exhaust the 1550-byte buffers on an
  affecte…
severity: medium
cvss: 6.8
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H'
cwe:
  - CWE-400
  - CWE-770
vendor: cisco
product: secure_firewall_threat_defense
affected:
  - adaptive_security_appliance_software = 9.4(4)
  - adaptive_security_appliance_software = 9.8(2)
  - secure_firewall_threat_defense = 6.2.0
published: '2018-10-05'
updated: '2026-08-11'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2018-15399'
references:
  - url: 'http://www.securitytracker.com/id/1041785'
    label: psirt@cisco.com
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20181003-asa-syslog-dos
    label: psirt@cisco.com
  - url: 'http://www.securitytracker.com/id/1041785'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20181003-asa-syslog-dos
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.01842
epssPercentile: 0.77748
ingestedAt: '2026-08-11T19:48:25.943Z'
---

## Overview

A vulnerability in the TCP syslog module of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to exhaust the 1550-byte buffers on an affected device, resulting in a denial of service (DoS) condition. The vulnerability is due to a missing boundary check in an internal function. An attacker could exploit this vulnerability by establishing a man-in-the-middle position between an affected device and its configured TCP syslog server and then maliciously modifying the TCP header in segments that are sent from the syslog server to the affected device. A successful exploit could allow the attacker to exhaust buffer on the affected device and cause all TCP-based features to stop functioning, resulting in a DoS condition. The affected TCP-based features include AnyConnect SSL VPN, clientless SSL VPN, and management connections such as Secure Shell (SSH), Telnet, and HTTPS.

## Affected

- `adaptive_security_appliance_software = 9.4(4)`
- `adaptive_security_appliance_software = 9.8(2)`
- `secure_firewall_threat_defense = 6.2.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.