Code execution via over-expanding Tight framebuffer update
Published Aug 21, 2026 · Updated Aug 21, 2026
Heap buffer overflow in LibVNCClient 0.9.12 through 0.9.15 allows remote attackers to crash clients or execute code via a VNC server. HandleTightBPP passes decompressed row batches to framebuffer filters before checking whether the server-controlled zlib stream exceeds the rectangle height. Exploitation requires a client to connect to a malicious server or a man-in-the-middle to alter the session; default builds are exposed, while reliable targeted code execution under ASLR additionally requires an information leak.
Summary
What happened
Heap buffer overflow in LibVNCClient 0.9.12 through 0.9.15 allows remote attackers to crash clients or execute code via a VNC server. HandleTightBPP passes decompressed row batches to framebuffer filters before checking whether the server-controlled zlib stream exceeds the rectangle height. Exploitation requires a client to connect to a malicious server or a man-in-the-middle to alter the session; default builds are exposed, while reliable targeted code execution under ASLR additionally requires an information leak.
The record
- CVE
- CVE-2026-50538
- Published
- Aug 21, 2026
- Updated
- Aug 21, 2026
- Vendor
- LibVNC
- Product
- LibVNCServer
- Classifications
- CWE-122, CWE-787, T1203
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 21, 2026CVE publishedPublication date reported by the CVE source.
- Aug 21, 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=>= 0.9.12, <= 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.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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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