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Adaptive Security Appliance SoftwareOperating system · Cisco

CVE-2018-15399

MEDIUM · 6.8 CVSS v3.1 Published 2018-10-05
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
77/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A boundary check missing in the TCP syslog module of Cisco ASA and FTD software allows an attacker with MITM positioning between the device and its syslog server to maliciously modify TCP headers from the syslog server, exhausting the 1550-byte buffers and causing all TCP-based features (VPN, SSH, Telnet, HTTPS) to fail.

MitigationApply the relevant Cisco software update when available. As a workaround, consider using UDP syslog instead of TCP if operationally feasible, or implement network controls to prevent MITM attacks on the syslog path.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Adaptive Security Appliance SoftwareOperating system
Affected:= 9.4\(4\)= 9.8\(2\)
Secure Firewall Threat DefenseApplication
Affected:= 6.2.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Cisco ASA or FTD device and version
    Run 'show version' on the ASA CLI or use 'show version' in FTD CLI. Look for 'Cisco Adaptive Security Appliance' or 'Cisco Firepower Threat Defense' in the output and note the version number.
    Affected if Version is 9.4(4), 9.8(2), or 6.2.0 exactly as listed in the affected versions.
  2. Confirm TCP syslog is enabled
    Run 'show run all logging' or 'show logging' and examine the output for 'logging server' commands using the 'tcp' protocol. Look for lines like 'logging server <ip> tcp/<port>' or 'logging host <interface> tcp <ip>'
    Affected if A logging server is configured with the 'tcp' protocol rather than 'udp'.
  3. Check for active syslog configuration
    Run 'show logging' to display the current syslog configuration and operational status. Verify if syslog is actively configured and pointing to a remote server.
    Affected if Syslog is configured and pointing to a remote server over TCP.

The device is affected if it runs Cisco ASA version 9.4(4), 9.8(2), or FTD version 6.2.0 AND has a TCP-based syslog server configured.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the relevant Cisco software update when available. As a workaround, consider using UDP syslog instead of TCP if operationally feasible, or implement network controls to prevent MITM attacks on the syslog path.

Fix this in Adaptive Security Appliance Software Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,640
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2018-15399 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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