Pre-authentication code execution via unchecked URI copy
Published Jul 1, 2026 · Updated Jul 1, 2026
Global buffer overflow in UltraVNC repeater 1.8.2.2 and earlier allows remote attackers to execute arbitrary code via a long HTTP URI. wi_senderr() and wi_replyhdr() pass the request URI to unchecked sprintf calls that copy it into the fixed 1000-byte global hdrbuf. The overflow occurs before authentication when the repeater HTTP administration port is reachable, corrupting adjacent global state and enabling code execution on the Windows host.
Summary
What happened
Global buffer overflow in UltraVNC repeater 1.8.2.2 and earlier allows remote attackers to execute arbitrary code via a long HTTP URI. wi_senderr() and wi_replyhdr() pass the request URI to unchecked sprintf calls that copy it into the fixed 1000-byte global hdrbuf. The overflow occurs before authentication when the repeater HTTP administration port is reachable, corrupting adjacent global state and enabling code execution on the Windows host.
The record
- CVE
- CVE-2026-7840
- Published
- Jul 1, 2026
- Updated
- Jul 1, 2026
- Vendor
- UltraVNC Team
- Product
- UltraVNC
- Classifications
- CWE-787, T1210
- 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.
Public exploit references
- Securin crash-trigger proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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