Vulnerability Details CVE-2026-44042
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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.003
EPSS Ranking 23.1%
CVSS Severity
CVSS v3 Score 3.7
Products affected by CVE-2026-44042
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cpe:2.3:a:uvnc:ultravnc:1.0.9.6.2
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cpe:2.3:a:uvnc:ultravnc:1.1.8.9
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cpe:2.3:a:uvnc:ultravnc:1.1.9.3
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cpe:2.3:a:uvnc:ultravnc:1.1.9.6
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cpe:2.3:a:uvnc:ultravnc:1.2.0.5
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cpe:2.3:a:uvnc:ultravnc:1.2.0.9
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cpe:2.3:a:uvnc:ultravnc:1.2.1.0
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cpe:2.3:a:uvnc:ultravnc:1.2.1.2
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cpe:2.3:a:uvnc:ultravnc:1.2.1.6
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cpe:2.3:a:uvnc:ultravnc:1.2.1.7
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cpe:2.3:a:uvnc:ultravnc:1.2.2.2
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cpe:2.3:a:uvnc:ultravnc:1.2.2.3
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cpe:2.3:a:uvnc:ultravnc:1.2.2.4
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cpe:2.3:a:uvnc:ultravnc:1.2.4.0
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cpe:2.3:a:uvnc:ultravnc:1.3.2
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cpe:2.3:a:uvnc:ultravnc:1.3.4
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cpe:2.3:a:uvnc:ultravnc:1.3.4.1
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cpe:2.3:a:uvnc:ultravnc:1.3.4.2
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cpe:2.3:a:uvnc:ultravnc:1.3.6.0
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cpe:2.3:a:uvnc:ultravnc:1.3.8.0
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cpe:2.3:a:uvnc:ultravnc:1.3.8.1
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cpe:2.3:a:uvnc:ultravnc:1.4.0.5
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cpe:2.3:a:uvnc:ultravnc:1.4.0.6
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cpe:2.3:a:uvnc:ultravnc:1.4.0.9
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cpe:2.3:a:uvnc:ultravnc:1.4.2.0
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cpe:2.3:a:uvnc:ultravnc:1.4.3.0
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cpe:2.3:a:uvnc:ultravnc:1.4.3.1
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cpe:2.3:a:uvnc:ultravnc:1.4.3.5
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cpe:2.3:a:uvnc:ultravnc:1.4.3.6
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cpe:2.3:a:uvnc:ultravnc:1.5.0.0
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cpe:2.3:a:uvnc:ultravnc:1.6.0.0
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cpe:2.3:a:uvnc:ultravnc:1.6.1.0
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cpe:2.3:a:uvnc:ultravnc:1.6.4.0
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cpe:2.3:a:uvnc:ultravnc:1.8.2.2