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CVE-2026-44042

3.7 · LOW

UltraVNC repeater through 1.8.2.2 contains an off-by-one error in the Base64 decode helper used for HTTP Basic authentication.

Published Jul 1, 2026CWE-193EPSS 0.49%

Overview

CVE-2026-44042 is a low-severity vulnerability. It was published on July 1, 2026 and has a CVSS 3.1 base score of 3.7 (LOW).

This vulnerability has a CVSS 3.1 base score of 3.7, rated LOW. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/ultravnc/UltraVNCRefuvnc.com/Refwww.securin.io/zero-days/cve-2026-44042-wi-uudecode-off-by-one-bounded-ultravnc-repeater

How CyberStrike helps

Frequently asked questions

What is CVE-2026-44042?

CVE-2026-44042 is a low-severity vulnerability. It was published on July 1, 2026 and has a CVSS 3.1 base score of 3.7 (LOW).

How severe is CVE-2026-44042?

This vulnerability has a CVSS 3.1 base score of 3.7, rated LOW. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-44042?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-44042?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-44042 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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