Heap corruption via RFB reason-length integer overflow
Published Jul 1, 2026 · Updated Jul 1, 2026
Heap buffer overflow in UltraVNC Viewer 1.8.2.2 and earlier allows remote attackers to corrupt memory via a malicious RFB server. ClientConnection.cpp adds one to the network-supplied 32-bit reasonLen before sizing a buffer; 0xFFFFFFFF wraps to zero, but ReadString retains the original length. Successful authentication is unnecessary, but the victim must connect to the server; the demonstrated outcome is a viewer crash, while code execution is not publicly demonstrated.
Summary
What happened
Heap buffer overflow in UltraVNC Viewer 1.8.2.2 and earlier allows remote attackers to corrupt memory via a malicious RFB server. ClientConnection.cpp adds one to the network-supplied 32-bit reasonLen before sizing a buffer; 0xFFFFFFFF wraps to zero, but ReadString retains the original length. Successful authentication is unnecessary, but the victim must connect to the server; the demonstrated outcome is a viewer crash, while code execution is not publicly demonstrated.
The record
- CVE
- CVE-2026-7838
- Published
- Jul 1, 2026
- Updated
- Jul 1, 2026
- Vendor
- UltraVNC Team
- Product
- UltraVNC
- Classifications
- CWE-787, CWE-190, T1203
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 1, 2026CVE publishedPublication date reported by the CVE source.
- Jul 1, 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 <=1.8.2.2
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
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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