CVE-2018-20177 – CVE-2018-20177 is a critical integer overflow v... (How to Fix)

Q: What is the severity of CVE-2018-20177?

CVE-2018-20177 has a CVSS score of 9.8 (CRITICAL). CVE-2018-20177 is a critical integer overflow vulnerability in rdesktop RDP client that leads to heap-based buffer overflow and remote code execution. Attackers can exploit this by sending specially crafted RDP packets to compromise vulnerable clients. All users running rdesktop versions up to v1.8.3 are affected.

📋 TL;DR

CVE-2018-20177 is a critical integer overflow vulnerability in rdesktop RDP client that leads to heap-based buffer overflow and remote code execution. Attackers can exploit this by sending specially crafted RDP packets to compromise vulnerable clients. All users running rdesktop versions up to v1.8.3 are affected.

💻 Affected Systems

Products:

rdesktop

Versions: All versions up to and including v1.8.3

Operating Systems: Linux, Unix-like systems, macOS

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects rdesktop client, not Windows RDP server. Vulnerability is in client-side parsing of server responses.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution with SYSTEM/root privileges, allowing complete compromise of the client system and potential lateral movement.

🟠

Likely Case

Remote code execution leading to malware installation, data theft, or system compromise.

🟢

If Mitigated

Denial of service or application crash if exploit fails or controls block execution.

🌐 Internet-Facing: HIGH - RDP clients often connect to internet-facing servers, making them vulnerable to malicious RDP servers.

🏢 Internal Only: MEDIUM - Internal RDP servers could be compromised and used to attack vulnerable clients.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: CONFIRMED

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Check Point Research published detailed analysis and exploit methodology. Attack requires client to connect to malicious RDP server.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: v1.8.4 and later

Vendor Advisory: https://github.com/rdesktop/rdesktop/commit/4dca546d04321a610c1835010b5dad85163b65e1

Restart Required: Yes

Instructions:

1. Update rdesktop to v1.8.4 or later. 2. For Linux distributions, use package manager: 'sudo apt update && sudo apt upgrade rdesktop' (Debian/Ubuntu) or 'sudo yum update rdesktop' (RHEL/CentOS). 3. Restart any active rdesktop sessions.

🔧 Temporary Workarounds

Network Segmentation

linux

Restrict RDP connections to trusted servers only using firewall rules.

iptables -A OUTPUT -p tcp --dport 3389 -d TRUSTED_SERVER_IP -j ACCEPT
iptables -A OUTPUT -p tcp --dport 3389 -j DROP

Use Alternative RDP Client

linux

Temporarily switch to alternative RDP clients like FreeRDP or Remmina until patched.

sudo apt install freerdp2-x11
sudo apt install remmina

🧯 If You Can't Patch

Disable rdesktop usage entirely and use alternative RDP clients
Implement strict network controls to only allow RDP connections to verified, trusted servers

🔍 How to Verify

Check if Vulnerable:

Check rdesktop version: 'rdesktop --version' or 'dpkg -l | grep rdesktop' or 'rpm -qa | grep rdesktop'

Check Version:

rdesktop --version

Verify Fix Applied:

Confirm version is 1.8.4 or higher: 'rdesktop --version | grep -q "1\.8\.[4-9]\|1\.9\|2\." && echo "Patched"'

📡 Detection & Monitoring

Log Indicators:

rdesktop crash logs
segmentation fault errors in system logs
unexpected process termination

Network Indicators:

RDP connections to unknown/untrusted servers
unusual RDP traffic patterns

SIEM Query:

process_name="rdesktop" AND (event_type="crash" OR exit_code="139")

📊 Metadata

CVE ID: CVE-2018-20177

CVSS v3 Score: 9.8 (CRITICAL)

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

CWE: CWE-190

Published: March 15, 2019

Last Updated: November 21, 2024

🔗 References

http://lists.opensuse.org/opensuse-security-announce/2019-09/msg00040.html Mailing List,Third Party Advisory
http://www.securityfocus.com/bid/106938 Broken Link,Third Party Advisory,VDB Entry
https://github.com/rdesktop/rdesktop/commit/4dca546d04321a610c1835010b5dad85163b65e1 Patch
https://lists.debian.org/debian-lts-announce/2019/02/msg00030.html Mailing List,Third Party Advisory
https://research.checkpoint.com/reverse-rdp-attack-code-execution-on-rdp-clients/ Exploit,Third Party Advisory
https://security.gentoo.org/glsa/201903-06 Third Party Advisory
https://www.debian.org/security/2019/dsa-4394 Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2019-09/msg00040.html Mailing List,Third Party Advisory
http://www.securityfocus.com/bid/106938 Broken Link,Third Party Advisory,VDB Entry
https://github.com/rdesktop/rdesktop/commit/4dca546d04321a610c1835010b5dad85163b65e1 Patch
https://lists.debian.org/debian-lts-announce/2019/02/msg00030.html Mailing List,Third Party Advisory
https://research.checkpoint.com/reverse-rdp-attack-code-execution-on-rdp-clients/ Exploit,Third Party Advisory
https://security.gentoo.org/glsa/201903-06 Third Party Advisory
https://www.debian.org/security/2019/dsa-4394 Third Party Advisory

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