What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-01 · updated 2026-10-25
• Weakness: CWE-125

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.

Affected products

• Kaspersky Lab UltraVNC: through 1.8.2.2

References

• https://github.com/ultravnc/UltraVNC
• https://uvnc.com/
• https://www.securin.io/zero-days/cve-2026-44041-vncwc2mb-wcslen-before-bounds-check-ultravnc

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