CVE-2026-44042

LOW

UltraVNC repeater wi_uudecode off-by-one in base64 decode boundary check

Title source: cna
STIX 2.1

Exploitation Summary

EIP tracks 1 public exploit for CVE-2026-44042. PoCs published by HermesNA-1.

AI-analyzed exploit summary This repository contains an auto-generated stub module for CVE-2026-44042, an off-by-one error in UltraVNC repeater's Base64 decode helper for HTTP Basic authentication. The code includes placeholder methods (`check` and `run`) but lacks actual exploit implementation or technical depth.

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.

Exploits (1)

github STUB 1 stars
by HermesNA-1 · pythonpoc
https://github.com/HermesNA-1/SnakeSploit/tree/main/data/modules_generated/cve-2026-44042_ultravnc_repeater_through.py

This repository contains an auto-generated stub module for CVE-2026-44042, an off-by-one error in UltraVNC repeater's Base64 decode helper for HTTP Basic authentication. The code includes placeholder methods (`check` and `run`) but lacks actual exploit implementation or technical depth.

Classification
Stub 98%
Attack Type
Other
Complexity
Moderate
Reliability
Theoretical
Target: UltraVNC repeater through 1.8.2.2
No auth needed
Prerequisites: Network access to UltraVNC repeater's HTTP port · Knowledge of the vulnerable Base64 decoding logic (not provided in the stub)
mistral-large-3 · analyzed Jul 09, 2026 Full analysis →

References (3)

Core 3
Core References
Vendor Advisory vendor-advisory
UltraVNC project page
https://uvnc.com/
Product product
UltraVNC source repository
https://github.com/ultravnc/UltraVNC

Scores

CVSS v3 3.7
EPSS 0.0039
EPSS Percentile 31.6%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

CISA SSVC

Vulnrichment
Exploitation none
Automatable no
Technical Impact partial

Details

CWE
CWE-193
Status published
Products (2)
uvnc/UltraVNC < 1.8.2.2
uvnc/ultravnc < 1.8.2.2
Published Jul 01, 2026
Tracked Since Jul 01, 2026