Summary Two filter-bypass techniques in "NukeViet\Core\Request::filterAttr()" and "NukeViet\Core\Request::unhtmlentities()" allow a low-privileged user (any account with news post permission) to store and serve arbitrary JavaScript to any visitor of the affected page. Affected Component "vendor/vinades/nukeviet/Core/Request.php" — class "NukeViet\Core\Request" Vulnerability Details Bypass 1 — Form Feed character prefix ("\x0C") before event handler name The "filterAttr()" method blocks event-handler attributes using: preg_match('/^on/i', $attrSubSet[0]) PHP's "trim()" does not strip the ASCII Form Feed character ("\x0C", U+000C). An attacker can prefix the attribute name with "\x0C" so that "\x0Conerror" does not match "/^on/". The HTML5 browser parser treats "\x0C" as a valid whitespace separator and correctly activates the event handler. Proof-of-concept payload (URL-encoded POST body field "bodyhtml"): <img src="x" %0Conerror="alert('XSS')"> Bypass 2 — Decimal HTML entity tab (" ") inside "javascript:" URI "unhtmlentities()" strips the hex-encoded tab " " via "str_ireplace", but did not strip its decimal equivalent " ". The keyword-blocking regex "/j\sa\sv\sa\ss\sc\sr\si\sp\st/si" uses "\s" which does not match HTML entities. The value "jav ascript:alert()" passes the filter, is stored in the database, and is decoded by the browser into a working "javascript:" URI. Proof-of-concept payload (inside a Markdown-style link): "Click me" (jav ascript:alert('XSS')) Impact An authenticated attacker with news-posting permission can inject persistent JavaScript that executes in the browser of any user (including administrators) who views the affected article. This enables session cookie theft, credential harvesting, defacement, and further privilege escalation. Patches Fixed in commit "<commit-sha>" by modifying "vendor/vinades/nukeviet/Core/Request.php": 1. "filterAttr()" — strip all ASCII control characters ("\x00"–"\x20") from the attribute name before the "/^on/" check: $attrSubSet[0] = preg_replace('/[\x00-\x20]/', '', strtolower($attrSubSet[0])); 2. "unhtmlentities()" — strip decimal HTML entities for all ASCII control characters (0–31) before the keyword checks: $value = preg_replace('/&#0*(?:3[01]|[12][0-9]|[0-9]);/', '', $value); Workarounds None. Update to the patched version. Resources - CWE-79: Improper Neutralization of Input During Web Page Generation (Cross-site Scripting) - OWASP WSTG-INPV-02: Testing for Stored Cross Site Scripting - "OWASP Top 10 A03:2021 – Injection" (https://owasp.org/Top10/A03_2021-Injection/)