CVE-2018-0101 – This critical vulnerability in Cisco ASA SSL VP... (How to Fix)

Q: What is the severity of CVE-2018-0101?

CVE-2018-0101 has a CVSS score of 10.0 (CRITICAL). This critical vulnerability in Cisco ASA SSL VPN allows unauthenticated remote attackers to execute arbitrary code or cause system reloads via crafted XML packets. It affects multiple Cisco ASA and Firepower products with webvpn enabled. Attackers can gain full system control without authentication.

📋 TL;DR

This critical vulnerability in Cisco ASA SSL VPN allows unauthenticated remote attackers to execute arbitrary code or cause system reloads via crafted XML packets. It affects multiple Cisco ASA and Firepower products with webvpn enabled. Attackers can gain full system control without authentication.

💻 Affected Systems

Products:

Cisco ASA 3000 Series ISA
ASA 5500 Series
ASA 5500-X Series
ASA Services Module
ASA 1000V Cloud Firewall
Adaptive Security Virtual Appliance (ASAv)
Firepower 2100 Series
Firepower 4110
Firepower 9300 ASA Security Module
Firepower Threat Defense Software (FTD)

Versions: Multiple versions prior to fixes released in January 2018

Operating Systems: Cisco ASA OS

Default Config Vulnerable: ⚠️ Yes

Notes: Requires webvpn feature to be enabled. Affects both physical and virtual appliances.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete system compromise with remote code execution, allowing attacker to gain full administrative control of the ASA device and pivot to internal networks.

🟠

Likely Case

Denial of service through system reloads, potentially disrupting VPN connectivity and network security functions.

🟢

If Mitigated

Limited impact if webvpn is disabled or proper network segmentation isolates vulnerable devices.

🌐 Internet-Facing: HIGH - Directly exploitable from internet when webvpn interface is exposed.

🏢 Internal Only: MEDIUM - Still exploitable from internal networks but requires network access.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: CONFIRMED

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploit code publicly available. Multiple proof-of-concepts demonstrate reliable exploitation.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Multiple fixed versions depending on platform - see Cisco advisory for specific versions

Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180129-asa1

Restart Required: Yes

Instructions:

1. Check current ASA version with 'show version'. 2. Download appropriate fixed version from Cisco. 3. Upload new image via TFTP/SCP. 4. Configure boot system. 5. Reload device.

🔧 Temporary Workarounds

Disable webvpn

all

Temporarily disable the vulnerable webvpn feature if immediate patching isn't possible

no webvpn
write memory

Restrict access to webvpn interface

all

Apply access control lists to limit connections to webvpn interface

access-list WEBVPN_ACL deny ip any any
access-group WEBVPN_ACL in interface outside

🧯 If You Can't Patch

Disable webvpn feature entirely if not required
Implement strict network segmentation to isolate vulnerable devices from untrusted networks

🔍 How to Verify

Check if Vulnerable:

Check if webvpn is enabled: 'show running-config | include webvpn'. Check ASA version against affected versions in Cisco advisory.

Check Version:

show version | include Software

Verify Fix Applied:

Verify ASA version is updated to fixed version: 'show version | include Software'. Confirm webvpn configuration if re-enabled.

📡 Detection & Monitoring

Log Indicators:

Multiple XML parsing errors in ASA logs
Unexpected system reloads
High volume of XML packets to webvpn interface

Network Indicators:

Multiple crafted XML packets to TCP/443 (webvpn)
Unusual traffic patterns to ASA webvpn interface

SIEM Query:

source="ASA" AND ("%ASA-3-722041" OR "webvpn" AND "XML")

📊 Metadata

CVE ID: CVE-2018-0101

CVSS v3 Score: 10.0 (CRITICAL)

CVSS Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

CWE: CWE-415

Published: January 29, 2018

Last Updated: November 21, 2024

🔗 References

http://www.securityfocus.com/bid/102845 Third Party Advisory,VDB Entry
http://www.securitytracker.com/id/1040292 Third Party Advisory,VDB Entry
https://icanthackit.wordpress.com/2018/01/30/thoughts-on-the-handling-cve-2018-0101-cisco-bug-cscvg35618/ Third Party Advisory
https://pastebin.com/YrBcG2Ln Exploit,Third Party Advisory
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180129-asa1 Vendor Advisory
https://www.exploit-db.com/exploits/43986/ Exploit,Third Party Advisory,VDB Entry
http://www.securityfocus.com/bid/102845 Third Party Advisory,VDB Entry
http://www.securitytracker.com/id/1040292 Third Party Advisory,VDB Entry
https://icanthackit.wordpress.com/2018/01/30/thoughts-on-the-handling-cve-2018-0101-cisco-bug-cscvg35618/ Third Party Advisory
https://pastebin.com/YrBcG2Ln Exploit,Third Party Advisory
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180129-asa1 Vendor Advisory
https://www.exploit-db.com/exploits/43986/ Exploit,Third Party Advisory,VDB Entry

📤 Share & Export

📄 Export Markdown 📋 Export JSON

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📋 TL;DR

💻 Affected Systems

📦 What is this software?

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Adaptive Security Appliance Software by Cisco

Adaptive Security Appliance Software by Cisco

Adaptive Security Appliance Software by Cisco

Adaptive Security Appliance Software by Cisco

Firepower Threat Defense by Cisco

Firepower Threat Defense by Cisco

Firepower Threat Defense by Cisco

Firepower Threat Defense by Cisco

Firepower Threat Defense by Cisco

Firepower Threat Defense by Cisco

⚠️ Risk & Real-World Impact

Worst Case

Likely Case

If Mitigated

🎯 Exploit Status

🛠️ Fix & Mitigation

✅ Official Fix

Instructions:

🔧 Temporary Workarounds

Disable webvpn

Restrict access to webvpn interface

🧯 If You Can't Patch

🔍 How to Verify

Check if Vulnerable:

Check Version:

Verify Fix Applied:

📡 Detection & Monitoring

Log Indicators:

Network Indicators:

SIEM Query:

📊 Metadata

🔗 References

📤 Share & Export

🔗 Related Vulnerabilities