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.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| uvnc | UltraVNC | unaffected |
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Project Subscriptions
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Advisories
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Fixes
Solution
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Workaround
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References
| Link | Providers |
|---|---|
| https://github.com/ultravnc/UltraVNC |
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| https://uvnc.com/ |
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History
Wed, 01 Jul 2026 05:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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. | |
| Title | UltraVNC repeater wi_uudecode off-by-one in base64 decode boundary check | |
| Weaknesses | CWE-193 | |
| References |
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| Metrics |
cvssV3_1
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Projects
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MITRE
Status: PUBLISHED
Assigner: securin
Published:
Updated: 2026-07-01T03:33:07.511Z
Reserved: 2026-05-05T03:40:37.003Z
Link: CVE-2026-44042
Vulnrichment
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NVD
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Redhat
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OpenCVE Enrichment
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Weaknesses