Debian dla-4755 : libvncclient1 - security update

medium Nessus Plugin ID 339429

Synopsis

The remote Debian host is missing one or more security-related updates.

Description

The remote Debian 11 host has packages installed that are affected by multiple vulnerabilities as referenced in the dla-4755 advisory.

- ------------------------------------------------------------------------- Debian LTS Advisory DLA-4755-1 [email protected] https://www.debian.org/lts/security/ Abhijith PA August 25, 2026 https://wiki.debian.org/LTS
- -------------------------------------------------------------------------

Package : libvncserver Version : 0.9.13+dfsg-2+deb11u2 CVE ID : CVE-2026-32853 CVE-2026-32854 CVE-2026-44988 CVE-2026-50538 Debian Bug : 1132016 1132017 1138174 1138253

Several vulnerabilities were discovered in libvncserver, a cross-platform library to implement VNC server or client functionality in program

CVE-2026-32853

a heap out-of-bounds read vulnerability in the UltraZip encoding handler that allows a malicious VNC server to cause information disclosure or application crash. Attackers can exploit improper bounds checking in the HandleUltraZipBPP() function by manipulating subrectangle header counts to read beyond the allocated heap buffer

CVE-2026-32854

null pointer dereference vulnerabilities in the HTTP proxy handlers within httpProcessInput() in httpd.c that allow remote attackers to cause a denial of service by sending specially crafted HTTP requests. Attackers can exploit missing validation of strchr() return values in the CONNECT and GET proxy handling paths to trigger null pointer dereferences and crash the server when httpd and proxy features are enabled.

CVE-2026-44988

LibVNCClient Tight Gradient decoding allows malicious server-triggered heap/stack out-of-bounds writes

CVE-2026-50538

a malicious (or man-in-the-middle) VNC server can force a connecting `libvncclient` to write attacker-controlled data past the end of its framebuffer. This is an out-of-bounds heap write with attacker-controlled length, contents, and offset.

For Debian 11 bullseye, these problems have been fixed in version 0.9.13+dfsg-2+deb11u2.

We recommend that you upgrade your libvncserver packages.

For the detailed security status of libvncserver please refer to its security tracker page at:
https://security-tracker.debian.org/tracker/libvncserver

Further information about Debian LTS security advisories, how to apply these updates to your system and frequently asked questions can be found at: https://wiki.debian.org/LTS

Tenable has extracted the preceding description block directly from the Debian security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

Solution

Upgrade the libvncclient1 packages.

Plugin Details

Severity: Medium

ID: 339429

File Name: debian_DLA-4755.nasl

Version: 1.1

Type: Local

Agent: unix

Family: Debian Local Security Checks

Published: 8/25/2026

Updated: 8/25/2026

Supported Sensors: Nessus Agent, Continuous Assessment, Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 4.9

Percentile: 57.96

CVSS v2

Risk Factor: High

Base Score: 9.4

Temporal Score: 7.4

Vector: CVSS2#AV:N/AC:L/Au:N/C:C/I:N/A:C

CVSS Score Source: CVE-2026-32853

CVSS v3

Risk Factor: High

Base Score: 8.1

Temporal Score: 7.3

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H

Temporal Vector: CVSS:3.0/E:P/RL:O/RC:C

CVSS v4

Risk Factor: Medium

Base Score: 6.9

Threat Score: 5.5

Threat Vector: CVSS:4.0/E:P

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N

Vulnerability Information

CPE: cpe:/o:debian:debian_linux:11.0, p-cpe:/a:debian:debian_linux:libvncclient1, p-cpe:/a:debian:debian_linux:libvncserver-dev, p-cpe:/a:debian:debian_linux:libvncserver1

Required KB Items: Host/local_checks_enabled, Host/Debian/release, Host/Debian/dpkg-l

Exploit Available: true

Exploit Ease: Exploits are available

Patch Publication Date: 8/25/2026

Vulnerability Publication Date: 3/24/2026

Reference Information

CVE: CVE-2026-32853, CVE-2026-32854, CVE-2026-44988, CVE-2026-50538

IAVA: 2026-A-0777

Detections

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