CVE-2026-44041 UltraVNC Wide String Out-of-Bounds Read
UltraVNC through 1.8.2.2 contains an out-of-bounds read in the wide-string to multibyte conversion helper. In rfb/dh.cpp:204, the vncWc2Mb() function passes a caller-supplied WCHAR pointer to wcslen() before any bounds check. If the caller provides a wide-character buffer that is not properly NUL-terminated, wcslen() reads past the end of the buffer until it encounters a NUL wchar, resulting in an out-of-bounds read. Under typical Win32 API usage this requires an abnormal caller contract. Impact is limited to a potential information disclosure from adjacent memory regions or a process crash (denial of service) if the over-read crosses a page boundary.
Quick answer
UltraVNC should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.
Who is affected
Affected versions
- <= 1.8.2.2
Fixed versions
- No vendor fix published yet
How to fix it
UltraVNC is affected and no public fixed version is listed in the local advisory data yet. Reduce access, disable risky features where possible, and apply the vendor fix when it is released.
- Check where UltraVNC is installed and whether it is reachable from the internet.
- Limit access to trusted users, trusted networks, or a VPN until a vendor fix is available.
- Disable the affected feature or module if the advisory points to a specific upload, login, admin, chat, or network service path.
- Watch the vendor or advisory source and apply the first supported fix as soon as it is released.
- Review logs for strange access, failed attempts, crashes, file uploads, or unexpected account changes.
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Verify the fix
- Confirm the installed version is no longer in the affected range.
- Retest the affected page, API, upload, login, chat, container, or network flow.
- Check logs after the change for blocked attempts, crashes, or errors.
- Run a fresh Fixnx scan and save the report.
Related categories
Trusted references
FAQ
What is affected by CVE-2026-44041?
UltraVNC versions listed as affected should be reviewed: <= 1.8.2.2.
What should I fix first?
Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.
How do I confirm the fix worked?
Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.
How are Fixnx security risk categories chosen?
Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.