CVE-2018-20181
📋 TL;DR
CVE-2018-20181 is a critical integer underflow 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. Anyone using rdesktop versions up to v1.8.3 is affected.
💻 Affected Systems
- rdesktop
📦 What is this software?
Rdesktop by Rdesktop
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise via remote code execution, allowing attacker to execute arbitrary code with user privileges, install malware, or pivot to other systems.
Likely Case
Remote code execution leading to credential theft, data exfiltration, or lateral movement within the network.
If Mitigated
Denial of service or application crash if exploit fails or controls limit execution.
🎯 Exploit Status
Check Point Research published detailed analysis and exploitation techniques. The vulnerability is in the client-side processing, so attackers can craft malicious RDP server responses.
🛠️ 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 version 1.8.4 or later using your package manager. 2. For Debian/Ubuntu: sudo apt update && sudo apt upgrade rdesktop. 3. For source installations: download latest from GitHub and compile. 4. Restart any active rdesktop sessions.
🔧 Temporary Workarounds
Disable seamless virtual channel
linuxDisable the seamless virtual channel feature which is vulnerable to this attack
rdesktop -seamless-disable
Use alternative RDP client
linuxTemporarily switch to FreeRDP or other RDP clients until patched
sudo apt install freerdp2-x11
🧯 If You Can't Patch
- Network segmentation: Isolate systems using rdesktop and restrict RDP traffic to trusted sources only
- Monitor for exploitation: Implement IDS/IPS rules to detect exploitation attempts and monitor for abnormal RDP traffic patterns
🔍 How to Verify
Check if Vulnerable:
Check rdesktop version: rdesktop --version | grep -E '1\.8\.[0-3]'Check Version:
rdesktop --versionVerify Fix Applied:
Verify version is 1.8.4 or higher: rdesktop --version | grep -E '1\.8\.[4-9]|1\.9|2\.'📡 Detection & Monitoring
Log Indicators:
- Application crashes of rdesktop
- Segmentation fault errors in system logs
- Abnormal process termination
Network Indicators:
- Unusual RDP traffic patterns
- RDP connections from unexpected sources
- Large or malformed RDP packets
SIEM Query:
source="*syslog*" AND ("segmentation fault" OR "rdesktop" AND "crash")🔗 References
- http://lists.opensuse.org/opensuse-security-announce/2019-09/msg00040.html
- http://www.securityfocus.com/bid/106938
- https://github.com/rdesktop/rdesktop/commit/4dca546d04321a610c1835010b5dad85163b65e1
- https://lists.debian.org/debian-lts-announce/2019/02/msg00030.html
- https://research.checkpoint.com/reverse-rdp-attack-code-execution-on-rdp-clients/
- https://security.gentoo.org/glsa/201903-06
- https://www.debian.org/security/2019/dsa-4394
- http://lists.opensuse.org/opensuse-security-announce/2019-09/msg00040.html
- http://www.securityfocus.com/bid/106938
- https://github.com/rdesktop/rdesktop/commit/4dca546d04321a610c1835010b5dad85163b65e1
- https://lists.debian.org/debian-lts-announce/2019/02/msg00030.html
- https://research.checkpoint.com/reverse-rdp-attack-code-execution-on-rdp-clients/
- https://security.gentoo.org/glsa/201903-06
- https://www.debian.org/security/2019/dsa-4394
