CVE-2026-44988: CWE-787: Out-of-bounds Write in LibVNC libvncserver
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.
AI Analysis
Technical Summary
LibVNCClient versions up to 0.9.15 contain an out-of-bounds write vulnerability (CWE-787) in the Tight encoding decoder's handling of the Gradient filter. The decoder uses fixed-size 2048-pixel scratch buffers but fails to reject rectangles with widths exceeding this size. A malicious VNC server can send a crafted FramebufferUpdate rectangle using Tight encoding with NoZlib | ExplicitFilter and the Gradient filter, causing the client to write beyond the allocated buffer. This memory corruption can impact confidentiality, integrity, and availability of the client system. The vulnerability is addressed by a specific commit (5b270544b85233668b98161323297d418a8f5fd1), but no explicit patch or vendor advisory is included in the provided data.
Potential Impact
Successful exploitation allows a malicious VNC server to cause out-of-bounds memory writes in the LibVNCClient-based client, potentially leading to arbitrary code execution, data corruption, or denial of service. The CVSS 3.1 score of 8.8 reflects high impact on confidentiality, integrity, and availability. There are no known exploits in the wild at this time.
Mitigation Recommendations
A fix for this vulnerability exists as indicated by the referenced commit. However, no official patch or vendor advisory details are provided in the input data. Users should update to a version of LibVNCClient that includes the fix from commit 5b270544b85233668b98161323297d418a8f5fd1 once it is released. Until then, patch status is not yet confirmed — check the vendor advisory or official project repository for current remediation guidance.
CVE-2026-44988: CWE-787: Out-of-bounds Write in LibVNC libvncserver
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.
CVSS v3.1
Score 8.8high
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
LibVNCClient versions up to 0.9.15 contain an out-of-bounds write vulnerability (CWE-787) in the Tight encoding decoder's handling of the Gradient filter. The decoder uses fixed-size 2048-pixel scratch buffers but fails to reject rectangles with widths exceeding this size. A malicious VNC server can send a crafted FramebufferUpdate rectangle using Tight encoding with NoZlib | ExplicitFilter and the Gradient filter, causing the client to write beyond the allocated buffer. This memory corruption can impact confidentiality, integrity, and availability of the client system. The vulnerability is addressed by a specific commit (5b270544b85233668b98161323297d418a8f5fd1), but no explicit patch or vendor advisory is included in the provided data.
Potential Impact
Successful exploitation allows a malicious VNC server to cause out-of-bounds memory writes in the LibVNCClient-based client, potentially leading to arbitrary code execution, data corruption, or denial of service. The CVSS 3.1 score of 8.8 reflects high impact on confidentiality, integrity, and availability. There are no known exploits in the wild at this time.
Mitigation Recommendations
A fix for this vulnerability exists as indicated by the referenced commit. However, no official patch or vendor advisory details are provided in the input data. Users should update to a version of LibVNCClient that includes the fix from commit 5b270544b85233668b98161323297d418a8f5fd1 once it is released. Until then, patch status is not yet confirmed — check the vendor advisory or official project repository for current remediation guidance.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-05-08T16:23:33.265Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a170b58e29bf47b50c90710
Added to database: 5/27/2026, 3:18:48 PM
Last enriched: 5/27/2026, 3:48:38 PM
Last updated: 5/29/2026, 2:59:32 PM
Views: 17
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