Heap disclosure or crash via unchecked subrectangle count
Published Mar 24, 2026 · Updated Mar 24, 2026
Heap out-of-bounds read in LibVNCClient 0.9.15 and earlier allows remote attackers controlling a VNC server to disclose heap data or crash the client. HandleUltraZipBPP treats the attacker-controlled outer-rectangle x field as a subrectangle count and advances through decompressed raw_buffer data without checking that each 12-byte header remains in bounds. Exploitation requires a LibVNCClient-based application to connect to the malicious server; UltraZip is registered by default, and the bounded outcomes are adjacent heap disclosure or a client crash.
Summary
What happened
Heap out-of-bounds read in LibVNCClient 0.9.15 and earlier allows remote attackers controlling a VNC server to disclose heap data or crash the client. HandleUltraZipBPP treats the attacker-controlled outer-rectangle x field as a subrectangle count and advances through decompressed raw_buffer data without checking that each 12-byte header remains in bounds. Exploitation requires a LibVNCClient-based application to connect to the malicious server; UltraZip is registered by default, and the bounded outcomes are adjacent heap disclosure or a client crash.
The record
- CVE
- CVE-2026-32853
- Published
- Mar 24, 2026
- Updated
- Mar 24, 2026
- Vendor
- LibVNC
- Product
- LibVNCServer
- Classifications
- CWE-125
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 24, 2026CVE publishedPublication date reported by the CVE source.
- Mar 24, 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 <=0.9.15
What conditions does exploitation require?
What is affected?
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
- Upstream UltraZip FramebufferUpdate proof of conceptproof of concept · unverified
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Technologies
Your stack
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Your stack
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