SB2020070625 - Fedora 32 update for libvncserver

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Main Vulnerability Database SB2020070625

SB2020070625 - Fedora 32 update for libvncserver

Published: July 6, 2020 Updated: April 25, 2025

Security Bulletin ID SB2020070625
CSH Severity
High
Patch available
YES
Number of vulnerabilities 4
Exploitation vector Remote access
Highest impact Code execution

Breakdown by Severity

High 25% Medium 75%
  • Low
  • Medium
  • High
  • Critical

Description

This security bulletin contains information about 4 vulnerabilities.


1) Buffer overflow (CVE-ID: CVE-2019-20839)

CWE-ID: CWE-119 - Memory corruption

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Green


The vulnerability allows a remote attacker to execute arbitrary code on the target system.

The vulnerability exists due to a boundary when processing long socket filename in libvncclient/sockets.c in LibVNCServer. A remote attacker can rick the victim to connect to server using a specially crafted configuration file, trigger buffer overflow and execute arbitrary code on the target system.


2) Buffer overflow (CVE-ID: CVE-2019-20840)

CWE-ID: CWE-119 - Memory corruption

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green


The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to a boundary error within hybiReadAndDecode() in libvncserver/ws_decode.c. A remote attacker can create a specially crafted request to the affected LibVNCServer installation and crash the service.


3) Memory leak (CVE-ID: CVE-2018-21247)

CWE-ID: CWE-401 - Missing release of memory after effective lifetime

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:U/U:Green


The vulnerability allows a remote attacker to gain access to sensitive information.

The vulnerability exists due memory leak within the ConnectToRFBRepeater() function in  libvncclient/rfbproto.c. A remote attacker can trick the victim to connect to a malicious VNC server, trigger the memory leak and gain access to sensitive information on the client's system.


4) Out-of-bounds write (CVE-ID: CVE-2017-18922)

CWE-ID: CWE-787 - Out-of-bounds write

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Amber


The vulnerability allows a remote non-authenticated attacker to execute arbitrary code.

It was discovered that websockets.c in LibVNCServer prior to 0.9.12 did not properly decode certain WebSocket frames. A malicious attacker could exploit this by sending specially crafted WebSocket frames to a server, causing a heap-based buffer overflow.


Remediation

Install update from vendor's website.

References