CVE-2026-44041 UltraVNC vncWc2Mb calls wcslen() before validating that the wide string is NUL-terminated

Medium 4.3 Published 1 Jul 2026 Updated 9 Jul 2026

An out-of-bounds read in UltraVNC's string conversion helper can leak memory or crash the application if a non-terminated wide string is processed.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-44041?

CVE-2026-44041 is a medium-severity memory corruption vulnerability in uvnc UltraVNC, published on 1 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

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.

Weakness: CWE-125

Which versions are affected by CVE-2026-44041?

It affects 1 product.

Products include Uvnc Ultravnc.

How do I fix CVE-2026-44041?

No fix has been published for CVE-2026-44041 yet. Limit exposure of the affected software until one is available.

Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.

Is CVE-2026-44041 being exploited?

There is no known exploitation of CVE-2026-44041 in the wild and no public exploit code.

Sources

Also known as GHSA-f9fh-23qv-g394.