GHSA-GH7J-9W79-XM55

Vulnerability from github – Published: 2026-07-01 06:31 – Updated: 2026-07-01 06:31
VLAI
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 (>), 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.

Severity
3.7 (Low)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
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{
  "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": "2026-07-01T06:31:34Z",
  "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"
    }
  ],
  "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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