CVE-2026-44042: low-severity vulnerability in uvnc UltraVNC
UltraVNC repeater wi_uudecode off-by-one in base64 decode boundary check
Published · Updated
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8Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 3.7epss 0.5%
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.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
Affected products
uvnc · UltraVNCRelated CVEs — uvnc UltraVNC
In the same product, most dangerous first.
CVE-2026-7840CRITICALUltraVNC repeater HTTP server global buffer overflow via long URI (pre-auth RCE)EPSS 2.6%CVE-2026-7838HIGHUltraVNC viewer heap buffer overflow via integer overflow in RFB connection-failure reason lengthEPSS 1.9%CVE-2026-7828MEDIUMUltraVNC repeater integer overflow in win_log malloc leading to heap overflowEPSS 1.4%CVE-2026-7829HIGHUltraVNC repeater authenticated out-of-bounds write in rule parser via oversized tokenEPSS 0.9%CVE-2026-7831HIGHUltraVNC viewer off-by-one stack overflow in ServerInit desktop name parsingEPSS 0.7%CVE-2026-7839CRITICALUltraVNC repeater ships hardcoded default admin password allowing unauthenticated admin accessEPSS 0.7%