Vulnerability in Uvnc Ultravnc
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 3.7 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L.
EPSS exploit prediction
EPSS: 0.005 (40.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 40th percentile — 40.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000
Affected products
- Uvnc Ultravnc — versions 0
Weakness classification (CWE)
References
- 33c584b5-0579-4c06-b2a0-8d8329fcab9c (Product, vendor-advisory, Release Notes)
- 33c584b5-0579-4c06-b2a0-8d8329fcab9c (Product, product)
- 33c584b5-0579-4c06-b2a0-8d8329fcab9c
Frequently asked questions
- What is CVE-2026-44042?
- CVE-2026-44042 is a low-severity vulnerability in Uvnc Ultravnc, classified under Off-by-one Error. CVSS score: 3.7/10. Published 2026-07-01.
- How severe is CVE-2026-44042?
- Low severity. CVSS v3 base score is 3.7 out of 10.