Cisco ASA and FTD Web Interface Path Traversal and Denial of Service Vulnerability (CVE-2018-0296) Technical Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTCisco ASA Software and Cisco FTD Software running on devices with enabled web interfaces (SSL VPN, AnyConnect, Clientless Portal, etc.)
Unauthenticated, remote attackers can trigger an unexpected device reload (DoS) or view sensitive system information without authentication via directory traversal
Apply official software updates from Cisco immediately, restrict web interface access using ACLs, or disable unnecessary HTTP services
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Cisco has released official software updates to address this vulnerability. Administrators should verify their current version and upgrade to a patched release. Below is an example of upgrading the ASA software via CLI using a TFTP server.
# Verify the current running ASA software version
show version | include Software
# Download the patched ASA image from the TFTP server
copy tftp://10.1.1.50/asa984-20-lfbff-k8.spa disk0:/asa984-20-lfbff-k8.spa
# Configure the boot path to the new image and save configuration
no boot system disk0:/asa-old-image.spa
boot system disk0:/asa984-20-lfbff-k8.spa
write memory
# Reload the device to apply the patch
reload2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, restrict access to the web management interface (HTTP/HTTPS) to trusted IP addresses only, or disable the HTTP server on untrusted interfaces.
# Restrict HTTPS access to a trusted management subnet (e.g., 192.168.10.0/24) on the outside interface
no http 0.0.0.0 0.0.0.0 outside
http 192.168.10.0 255.255.255.0 outside
# Disable the HTTP server entirely if web services are not required
no http server enable
write memory3. Log Audit & IoC Verification Commands
Monitor the ASA syslog and active connections to detect potential exploitation attempts targeting the directory traversal paths.
# Search syslog for traversal patterns such as '+CSCOE+' or '+CSCOCLI+'
show log | include \+CSCOE\+
show log | include \+CSCOCLI\+
# Inspect active VPN sessions for anomalous connections
show vpn-sessiondb briefStop Exposing VPN Ports to the Internet — Switch to Zero-Trust Access
Eliminate public-facing VPN concentrators and firewall management ports with identity-first Zero-Trust Network Access.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2018-0296) exists in the web engine of Cisco Adaptive Security Appliance (ASA) and Cisco Firepower Threat Defense (FTD) software. The root cause is the lack of proper input validation of the HTTP URL requested by remote clients. Due to this flaw, the web parser fails to sanitize directory traversal sequences or specific URL structures, leading to improper input validation (CWE-20) and directory traversal (CWE-22) vulnerabilities.
2. Exploitation Mechanics & Attack Scenario
An unauthenticated, remote attacker can exploit this vulnerability by sending a specially crafted HTTP GET request to the affected device's active web port (typically HTTPS 443).
- Information Disclosure Scenario: On certain software releases, the ASA does not reload but instead processes the traversal request (e.g., targeting paths containing
/+CSCOE+/or+CSCOCLI+), allowing the attacker to view sensitive system information, active session details, and directory structures in plaintext. - Denial of Service (DoS) Scenario: On other software releases or memory states, processing the malformed HTTP request triggers a null pointer dereference or memory corruption within the web service process, causing the entire device to crash and reload unexpectedly, disrupting all active network traffic.
3. Infrastructure & Business Impact
As a CISA KEV-listed vulnerability with an EPSS score of 0.999, this flaw is actively and heavily exploited in the wild. Because Cisco ASA and FTD devices serve as critical perimeter firewalls and VPN gateways, a successful DoS attack directly leads to complete network downtime and business interruption. Furthermore, the disclosure of sensitive session information can be leveraged by threat actors to bypass authentication and gain unauthorized access to internal networks.
Official Vendor Advisories & References
A vulnerability in the web interface of the Cisco Adaptive Security Appliance (ASA) could allow an unauthenticated, remote attacker to cause an affected device to reload unexpectedly, resulting in a denial of service (DoS) condition. It is also possible on certain software releases that the ASA will not reload, but an attacker could view sensitive system information without authentication by using directory traversal techniques. The vulnerability is due to lack of proper input validation of the HTTP URL. An attacker could exploit this vulnerability by sending a crafted HTTP request to an affected device. An exploit could allow the attacker to cause a DoS condition or unauthenticated disclosure of information. This vulnerability applies to IPv4 and IPv6 HTTP traffic. This vulnerability affects Cisco ASA Software and Cisco Firepower Threat Defense (FTD) Software that is running on the following Cisco products: 3000 Series Industrial Security Appliance (ISA), ASA 1000V Cloud Firewall, ASA 5500 Series Adaptive Security Appliances, ASA 5500-X Series Next-Generation Firewalls, ASA Services Module for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers, Adaptive Security Virtual Appliance (ASAv), Firepower 2100 Series Security Appliance, Firepower 4100 Series Security Appliance, Firepower 9300 ASA Security Module, FTD Virtual (FTDv). Cisco Bug IDs: CSCvi16029.
Frequently Asked SecOps Questions (CVE-2018-0296)
FAQQ1. How critical is CVE-2018-0296 and is it actively exploited in the wild?
CVE-2018-0296 is rated CVSS 7.5 (HIGH) with a 30-day EPSS exploitation probability of 99.9%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2018-0296?
Primary impacted vendors include cisco across adaptive_security_appliance, firepower_threat_defense. Scope summary: Cisco ASA Software and Cisco FTD Software running on physical and virtual appliances (ASA 5500, 5500-X, ASAv, Firepower 2100/4100/9300) with the web interface enabled
Q3. What temporary mitigations or workarounds exist for CVE-2018-0296 before patching?
[Mitigation] Apply official software updates from Cisco immediately, restrict web interface access using ACLs, or disable unnecessary HTTP services Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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