Cybersecurity professionals consider CVE-2026-40262 an immediate threat requiring urgent mitigation.
Status: Received on 17 Apr 2026, 01:17 UTC
Published on: 17 Apr 2026, 01:17 UTC
CVSS Release: version 3
security-advisories@github.com
Secondary
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N
CVE-2026-40262: Note Mark is an open-source note-taking application. In versions 0.19.1 and prior, the asset delivery handler serves uploaded files inline and relies on magic-byte detection for content type, which does not identify text-based formats such as HTML, SVG, or XHTML. These files are served with an empty Content-Type, no X-Content-Type-Options: nosniff header, and inline disposition, allowing browsers to sniff and render active content. An authenticated user can upload an HTML or SVG file containing JavaScript as a note asset, and when a victim navigates to the asset URL, the script executes under the application's origin with access to the victim's authenticated session and API actions. This issue has been fixed in version 0.19.2.
The exploitability of CVE-2026-40262 depends on two key factors: attack complexity (the level of effort required to execute an exploit) and privileges required (the access level an attacker needs).
CVE-2026-40262 presents an accessible attack vector with minimal effort required. Restricting access controls and implementing security updates are critical to reducing exploitation risks.
A lower complexity and fewer privilege requirements make exploitation easier. Security teams should evaluate these aspects to determine the urgency of mitigation strategies, such as patch management and access control policies.
Attack Complexity (AC) measures the difficulty in executing an exploit. A high AC means that specific conditions must be met, making an attack more challenging, while a low AC means the vulnerability can be exploited with minimal effort.
Privileges Required (PR) determine the level of system access necessary for an attack. Vulnerabilities requiring no privileges are more accessible to attackers, whereas high privilege requirements limit exploitation to authorized users with elevated access.
Above is the CVSS Sub-score Breakdown for CVE-2026-40262, illustrating how Base, Impact, and Exploitability factors combine to form the overall severity rating. A higher sub-score typically indicates a more severe or easier-to-exploit vulnerability.
Below is the Impact Analysis for CVE-2026-40262, showing how Confidentiality, Integrity, and Availability might be affected if the vulnerability is exploited. Higher values usually signal greater potential damage.
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