CVE-2026-44042
LowCVSS 3.7Exploitation Probability (EPSS)
Low risk31th percentile - higher than 31% of all known CVEs
Summary
UltraVNC repeater up to version 1.8.2.2 contains an off-by-one error in the Base64 decode helper used for HTTP Basic authentication. The wi_uudecode() function in webutils.c:817 uses a strict greater-than comparison (>) instead of greater-than-or-equal (>=), leaving a latent vulnerability. Currently, the risk is limited to a one-byte write at the boundary of a 1024-byte stack buffer.
Risk Assessment
The risk for the organization is currently low, but the vulnerability could become exploitable if buffering constraints change in the future. It could potentially lead to data integrity issues or service disruption.
Recommendation
It is recommended to update UltraVNC repeater to the latest version that includes a fix for this bug. Monitor official sources for a security patch.
Original NVD description (English source)
UltraVNC repeater through 1.8.2.2 contains an off-by-one error in the Base64 decode helper used for HTTP Basic authentication. In repeater/webgui/webutils.c:817, the wi_uudecode() function checks whether the input length exceeds the output buffer with a strict greater-than comparison (>), while the correct check should be greater-than-or-equal (>=). When strlen(authdata) equals sizeof(decode), the decoded output length (approximately 3/4 of input) does not overflow the buffer in current practice because the outer HTTP request bounds constrain the Authorization header. However, the defective check leaves a latent off-by-one condition that could become exploitable if the buffering constraints change. The current risk is limited to a one-byte write at the boundary of a 1024-byte stack buffer under constrained conditions.