Libvncserver CVE-2020-25708

HIGH

Divide By Zero (CWE-369)

2020-11-27 secalert@redhat.com

Denial Of Service Debian Red Hat Debian Linux Enterprise Linux Libvncserver Libvncserver Project

7.5

CVSS 3.1 · NVD

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Vulnerability Assessment

Weakness	CWE CWE-369 OWASP Top 10:2025 A10:2025 - Mishandling of Exceptional Conditions ASVS 5.0 V16 - Security Logging and Error Handling Division safety checks
Impact	CVSS score of 7.5 (HIGH). Attack characteristics: network attack vector, low complexity, no privileges required, no user interaction not required. Public proof-of-concept exploit code is available.
Exploit ScenarioDerived	This vulnerability can be exploited remotely over the network. Successful exploitation could compromise the high-severity affected system.

This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).

No patch listed yet 1.6% exploitation probability (EPSS)

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AnalysisAI

A divide by zero issue was found to occur in libvncserver-0.9.12. Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

RemediationAI

No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Apply vendor patches when available. Implement network segmentation and monitoring as interim mitigations.

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Technical ContextAI · show details

This vulnerability is classified under CWE-369. A divide by zero issue was found to occur in libvncserver-0.9.12. A malicious client could use this flaw to send a specially crafted message that, when processed by the VNC server, would lead to a floating point exception, resulting in a denial of service. Affected products include: Libvncserver Project Libvncserver, Redhat Enterprise Linux, Debian Debian Linux.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 7.5 HIGH

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

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

DescriptionNVD

A divide by zero issue was found to occur in libvncserver-0.9.12. A malicious client could use this flaw to send a specially crafted message that, when processed by the VNC server, would lead to a floating point exception, resulting in a denial of service.

Threat Intelligence Overview

EPSS Score

1.6%

Top 27% exploitable

Exploit

POC

Public exploit code exists

Data Quality

2 sources

Confidence: Low

CVE.org

EPSS

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity HIGH

CISA KEV No

Public POC Yes

EPSS 1.6%

Patch available No

Active threat No

Deciding rule

HIGH severity (CVSS 7.0-8.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Scheduled

Exploitation· derived

Poc

System Exposure· derived

Open

Automatable· derived

Yes

Human Impact· derived

Medium

Priority Score

60

Low Medium High Critical

KEV: 0

EPSS: +2

CVSS: +38

PoC: +20

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Denial of Service MEDIUM

Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.

Affected Products (CPE)NVD

cpe:2.3:a:libvncserver_project:libvncserver:0.9.12:*:*:*:*:*:*:*

cpe:2.3:o:redhat:enterprise_linux:6.0:*:*:*:*:*:*:*

cpe:2.3:o:redhat:enterprise_linux:7.0:*:*:*:*:*:*:*

cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*

cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*

More in Libvncserver

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CVE-2018-7225 CRITICAL Act Now POC

An issue was discovered in LibVNCServer through 0.9.11. Rated critical severity (CVSS 9.8), this vulnerability is remote

CVE-2014-6052 HIGH This Week POC

The HandleRFBServerMessage function in libvncclient/rfbproto.c in LibVNCServer 0.9.9 and earlier does not check certain

CVE-2014-6053 MEDIUM This Month

The rfbProcessClientNormalMessage function in libvncserver/rfbserver.c in LibVNCServer 0.9.9 and earlier does not proper

CVE-2014-6054 MEDIUM This Month

The rfbProcessClientNormalMessage function in libvncserver/rfbserver.c in LibVNCServer 0.9.9 and earlier allows remote a

CVE-2016-9942 CRITICAL Act Now

Heap-based buffer overflow in ultra.c in LibVNCClient in LibVNCServer before 0.9.11 allows remote servers to cause a den

CVE-2016-9941 CRITICAL Act Now

Heap-based buffer overflow in rfbproto.c in LibVNCClient in LibVNCServer before 0.9.11 allows remote servers to cause a

CVE-2018-20020 CRITICAL Act Now

LibVNC before commit 7b1ef0ffc4815cab9a96c7278394152bdc89dc4d contains heap out-of-bound write vulnerability inside stru

CVE-2018-20019 CRITICAL Act Now

LibVNC before commit a83439b9fbe0f03c48eb94ed05729cb016f8b72f contains multiple heap out-of-bound write vulnerabilities

CVE-2018-15127 CRITICAL Act Now

LibVNC before commit 502821828ed00b4a2c4bef90683d0fd88ce495de contains heap out-of-bound write vulnerability in server c

CVE-2018-15126 CRITICAL Act Now

LibVNC before commit 73cb96fec028a576a5a24417b57723b55854ad7b contains heap use-after-free vulnerability in server code

CVE-2014-6051 HIGH This Week

Integer overflow in the MallocFrameBuffer function in vncviewer.c in LibVNCServer 0.9.9 and earlier allows remote VNC se

CVE-2014-6055 MEDIUM This Month

Multiple stack-based buffer overflows in the File Transfer feature in rfbserver.c in LibVNCServer 0.9.9 and earlier allo

Same weakness CWE-369 – Divide By Zero

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CVE-2017-11720 CRITICAL POC

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CVE-2016-3623 HIGH POC

CVE-2023-3896 HIGH POC

CVE-2023-1127 HIGH POC

CVE-2023-0512 HIGH POC

CVE-2021-29600 HIGH POC

Same technique Denial Of Service

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CVE-2015-5119 CRITICAL POC

CVE-2011-2462 CRITICAL POC

CVE-2011-0611 HIGH POC

CVE-2012-1889 HIGH POC

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CVE-2015-5122 CRITICAL POC

CVE-2011-0609 HIGH POC

References

Advisories & patches

REF https://lists.debian.org/debian-lts-announce/2022/09/msg00035.html

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