GHSA-GH7J-9W79-XM55
Vulnerability from github – Published: 2026-07-01 06:31 – Updated: 2026-07-09 06:31UltraVNC 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.
{
"affected": [],
"aliases": [
"CVE-2026-44042"
],
"database_specific": {
"cwe_ids": [
"CWE-193"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-07-01T05:16:21Z",
"severity": "LOW"
},
"details": "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 (\u003e), while the correct check should be greater-than-or-equal (\u003e=). 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.",
"id": "GHSA-gh7j-9w79-xm55",
"modified": "2026-07-09T06:31:59Z",
"published": "2026-07-01T06:31:34Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-44042"
},
{
"type": "WEB",
"url": "https://github.com/ultravnc/UltraVNC"
},
{
"type": "WEB",
"url": "https://uvnc.com"
},
{
"type": "WEB",
"url": "https://www.securin.io/zero-days/cve-2026-44042-wi-uudecode-off-by-one-bounded-ultravnc-repeater"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L",
"type": "CVSS_V3"
}
]
}
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