CVE-2026-44042: UltraVNC repeater wi_uudecode off-by-one in base64 decode boundary check
uvnc · UltraVNC
Vendor fix available · Affected: uvnc UltraVNC · Exploitation: unlikely (under 1%)
Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.
Higher than 42% of scored CVEs
DescriptionCVE.org
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.
Affected products1
From the CVE record. A product or version that is not listed is unknown, not unaffected.
- uvnc · UltraVNCup to and including 1.8.2.2
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CoverageNo articles yet
No CyberSIXT article names CVE-2026-44042 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.