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CVE-2026-44988— LibVNCClient Tight Gradient decoding allows malicious server-triggered heap/stack OOB writes

Quick assessment

Affected
LibVNC libvncserver
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

LibVNCServer是LibVNC开源的一款支持在程序中实现VNC（虚拟网络计算）服务器或客户端功能的跨平台C语言库。 LibVNCServer 0.9.15及之前版本存在缓冲区错误漏洞，该漏洞源于Tight编码解码器使用固定大小的2048像素暂存缓冲区用于Gradient过滤器，但未拒绝宽度大于2048像素的Tight矩形，可能导致缓冲区写入越界。

CVSS 8.8 · High EPSS 0.24% · P15

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
LibVNC libvncserver <= 0.9.15 affected
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I. Basic Information for CVE-2026-44988

Vulnerability Information
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Vulnerability Title
LibVNCClient Tight Gradient decoding allows malicious server-triggered heap/stack OOB writes
Source: CVE Program / CVE List V5
Vulnerability Description
LibVNCClient is a library for easy implementation of a VNC client. In 0.9.15 and earlier, LibVNCClient's Tight encoding decoder uses fixed-size 2048-pixel scratch buffers for the Gradient filter, but it does not reject Tight rectangles whose width is larger than 2048 pixels. A malicious VNC server can send a crafted FramebufferUpdate rectangle using Tight encoding with NoZlib | ExplicitFilter and the Gradient filter. When a LibVNCClient-based client connects, the client processes the server-controlled rectangle width and writes beyond fixed-size Gradient buffers. This vulnerability is fixed with commit 5b270544b85233668b98161323297d418a8f5fd1.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存写
Source: CVE Program / CVE List V5
Vulnerability Title
LibVNCServer 缓冲区错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
LibVNCServer是LibVNC开源的一款支持在程序中实现VNC（虚拟网络计算）服务器或客户端功能的跨平台C语言库。 LibVNCServer 0.9.15及之前版本存在缓冲区错误漏洞，该漏洞源于Tight编码解码器使用固定大小的2048像素暂存缓冲区用于Gradient过滤器，但未拒绝宽度大于2048像素的Tight矩形，可能导致缓冲区写入越界。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
LibVNC libvncserver <= 0.9.15 -

II. Public POCs for CVE-2026-44988

# POC Description Source Link Shenlong Link
AI-Generated POC Premium
Qwen3.6-35B-A3B · 10685 chars
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In-depth vulnerability mechanism
Trigger conditions & impact
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III. Intelligence Information for CVE-2026-44988

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Patches & Fixes for CVE-2026-44988 (1)

Vendor Advisories for CVE-2026-44988 (1)

IV. Related Vulnerabilities

Same product: libvncserver
Same vendor: LibVNC
Same weakness: CWE-787