Client memory corruption via oversized Gradient rectangles
Published May 27, 2026 · Updated May 27, 2026
Out-of-bounds writes in LibVNCClient 0.9.15 and earlier allow remote attackers to corrupt client memory via a malicious VNC server. In src/libvncclient/tight.c, the Gradient paths use the server-controlled rectangle width in memset, indexed writes, and memcpy against fixed 2048-pixel scratch buffers without enforcing that limit. A user or application must connect the client to a malicious or compromised server; the demonstrated result is heap and stack memory corruption with callback-pointer reach, not reliable code execution.
Summary
What happened
Out-of-bounds writes in LibVNCClient 0.9.15 and earlier allow remote attackers to corrupt client memory via a malicious VNC server. In src/libvncclient/tight.c, the Gradient paths use the server-controlled rectangle width in memset, indexed writes, and memcpy against fixed 2048-pixel scratch buffers without enforcing that limit. A user or application must connect the client to a malicious or compromised server; the demonstrated result is heap and stack memory corruption with callback-pointer reach, not reliable code execution.
The record
- CVE
- CVE-2026-44988
- Published
- May 27, 2026
- Updated
- May 27, 2026
- Vendor
- LibVNC
- Product
- LibVNCServer
- Classifications
- CWE-787, T1203
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 27, 2026CVE publishedPublication date reported by the CVE source.
- May 27, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=<= 0.9.15
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Public exploit references
- LibVNCClient Tight Gradient reproduction packageproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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