CVE-2026-44042
Uvnc Ultravnc ≤ 1.8.2.2
Raw vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:LSummary
CVE-2026-44042 is a low-severity Off-by-one Error (CWE-193) vulnerability in Uvnc Ultravnc. Its CVSS base score is 3.7 (Low).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 31th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-40877
Vulnerability Data
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…
more
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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Off-by-one flaw in HTTP Basic auth decoder of public-facing UltraVNC repeater enables remote exploitation of the service.
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
Mitigating Controls (NIST 800-53 r5) AI
Directly enforces correct length and bounds checks on untrusted Base64 input before wi_uudecode writes into the 1024-byte stack buffer.
Requires developer testing and fuzzing that would detect the off-by-one comparison (>) versus (>=) in the authentication decoder.
Mandates prompt patching of the latent CWE-193 flaw once the defective wi_uudecode check is identified.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly prevent off-by-one errors via reviews, static analysis, and testing.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development and acceptance can detect off-by-one errors before release.
Secure development life cycle includes requirements and reviews that can catch off-by-one errors.
Application security requirements can specify bounds-checking and input validation to prevent off-by-one errors.
Secure system architecture and engineering principles promote defensive coding practices that reduce off-by-one mistakes.
Secure coding directly addresses off-by-one errors through coding standards and peer review.