CVE-2026-44041: UltraVNC vncWc2Mb calls wcslen() before validating that the wide string is NUL-terminated
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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
UltraVNCto a version that resolves this vulnerability.Fixed in 1.8.2.2 - Compensating control
Ensure callers provide properly NUL-terminated WCHAR buffers to vncWc2Mb() (rfb/dh.cpp:204) to avoid wcslen() over-reading past the buffer end.
Event History
Frequently Asked Questions
What is CVE-2026-44041?
CVE-2026-44041 is a vulnerability in UltraVNC versions up to 1.8.2.2 that allows for an out-of-bounds read due to a lack of validation in the vncWc2Mb() function.
What is the severity of CVE-2026-44041?
The severity of CVE-2026-44041 is medium, rated at 6.5 on the CVSS scale.
How do I fix CVE-2026-44041?
To fix CVE-2026-44041, upgrade to UltraVNC version that has addressed this vulnerability.
What impact does CVE-2026-44041 have on UltraVNC users?
CVE-2026-44041 can lead to potential information disclosure due to an out-of-bounds read when processing wide strings in UltraVNC.
Is CVE-2026-44041 exploitable remotely?
Yes, CVE-2026-44041 is exploitable remotely as it involves a caller-supplied WCHAR pointer in UltraVNC.