Quantum Secular Labs / Blog / Advisories

CVE-2018-20749: Libvnc Project Libvncserver: Buffer overflow

CVE-2018-20749 is rated critical with a CVSS v3.1 base score of 9.8 and affects Libvnc Project Libvncserver, along with 8 other products in NVD’s configuration data. Per its scoring, it can be exploited over the network, without authentication, without any user interaction. The scored impact on confidentiality, integrity and availability is the highest available.

Vulnerability description

LibVNC before 0.9.12 contains a heap out-of-bounds write vulnerability in libvncserver/rfbserver.c. The fix for CVE-2018-15127 was incomplete.

Severity breakdown

CVSS v3.1 9.8: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack vector: Network. Exploitable remotely over the network, with no need for local or physical access.
Attack complexity: Low. No special conditions; the attack can be repeated reliably.
Privileges required: None. No account or prior access is needed.
User interaction: None. No action from any user is needed.
Scope: Unchanged. Impact stays within the vulnerable component.
Confidentiality impact: High. Total loss of confidentiality; sensitive data can be fully disclosed.
Integrity impact: High. Total loss of integrity; data or system state can be fully modified.
Availability impact: High. Total loss of availability; the component can be shut down.

Underlying weakness

CWE-787: Out-of-bounds Write

The product writes data past the end, or before the beginning, of the intended buffer.

Affected products

Libvnc Project Libvncserver: before 0.9.12
Canonical Ubuntu Linux: 14.04; 16.04; 18.04; 18.10
Debian Linux: 8.0; 9.0
Siemens Simatic Itc1500 Firmware: from 3.0.0.0 before 3.2.1.0
Siemens Simatic Itc1500 Pro Firmware: from 3.0.0.0 before 3.2.1.0
Siemens Simatic Itc1900 Firmware: from 3.0.0.0 before 3.2.1.0
Siemens Simatic Itc1900 Pro Firmware: from 3.0.0.0 before 3.2.1.0
Siemens Simatic Itc2200 Firmware: from 3.0.0.0 before 3.2.1.0
Siemens Simatic Itc2200 Pro Firmware: from 3.0.0.0 before 3.2.1.0