CVE-2020-15249: 
PHP vulnerability analysis and mitigation

October CMS, a free, open-source, self-hosted CMS platform based on the Laravel PHP Framework, was affected by a stored XSS vulnerability (CVE-2020-15249) discovered in versions 1.0.319 through 1.0.469. The vulnerability allowed backend users with file upload permissions to upload unsanitized SVG files that could potentially contain malicious JavaScript code (GitHub Advisory).

The vulnerability existed due to lack of SVG file sanitization in the file upload functionality. Since SVG files can be parsed as HTML by browsers, attackers could embed JavaScript code within SVG files and upload them to paths under the website's domain (e.g., /storage/app/media/evil.svg). However, exploitation required the target to directly visit the malicious SVG file's URL in their browser, as the backend only displayed SVGs as image resources and did not render them inline (GitHub Advisory).

The impact of this vulnerability was considered Low severity. While it could potentially allow execution of arbitrary JavaScript code under the website's domain, successful exploitation required both authenticated access to the backend with file upload permissions and social engineering to convince targets to directly visit the malicious SVG file URL (GitHub Advisory).

Exploitation of this vulnerability required an attacker to have valid backend user credentials with file upload permissions. Additionally, since the backend did not display SVGs inline, the attacker would need to convince their target to visit the malicious SVG file's URL directly in their browser (GitHub Advisory).

The vulnerability was patched in October CMS version 1.0.469 and version 1.1.0. For users unable to upgrade, the recommended workaround is to manually apply the patch from commit 80aab47 to their installation (GitHub Advisory, GitHub Commit).