CVE-2026-75831

Grav before 2.0.15 contains a stored cross-site scripting vulnerability in the audio and video media rendering through the sourceParsedownElement method. The media URL fragment is concatenated unescaped into rawHtml source elements, allowing attackers to inject arbitrary HTML and JavaScript that executes in viewers' sessions.

Grav before 2.0.15 contains a stored cross-site scripting vulnerability in the audio and video media rendering through the sourceParsedownElement method. The media URL fragment is concatenated unescaped into rawHtml source elements, allowing attackers to inject arbitrary HTML and JavaScript that executes in viewers' sessions.

Target: github.com/getgrav/grav
Affected resource: Grav\Common\Media\Traits\AudioMediaTrait / VideoMediaTrait sourceParsedownElement() — verified on 2.0.13 (latest stable) and develop HEAD 5a7070f
Severity: Medium (~6.9 CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:L/A:N — anchored to the sibling script-XSS advisory CVE-2026-42841, same PR:H / S:C / C:H / I:L)
Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

Summary

A Markdown audio or video embed renders its <source> element as raw HTML with the media URL concatenated unescaped. The URL fragment is reflected without any encoding, so ![x](song.mp3#"><svg/onload=alert(1)>) breaks out of <source src="…"> and injects arbitrary HTML — including a script-executing <svg onload> — into the rendered page. Any user who views the page runs the attacker's JavaScript in their session; a logged-in administrator who views it exposes their same-origin Grav Admin session to the attacker's script.

This is the next sink in the media-parameter injection class the maintainer has been closing: GHSA-r7fx-8g49-7hhr (attribute()), GHSA-pmf8-g7c8-7v54 / CVE-2026-55890 (style(), 2.0.0-rc.9), and GHSA-ffmg-hfvg-jhg9 (resize(), 2.0.0-rc.10). All three guarded image style/attribute sinks; the aba291a5 audit scoped itself to "sinks reaching the style attribute" and did not cover the audio/video <source> rawHtml sink, which reaches full script execution rather than CSS injection.

Root Cause

The audio/video player builds its inner source as Parsedown rawHtml (emitted verbatim, unescaped), concatenating the media URL directly into a double-quoted attribute — AudioMediaTrait.php L43-52 (identical in VideoMediaTrait.php L58-67):

protected function sourceParsedownElement(array $attributes, $reset = true)
{
    $location = $this->url($reset);
    return [
        'name' => 'audio',
        'rawHtml' => '<source src="' . $location . '">Your browser does not support the audio tag.',
        'attributes' => $attributes
    ];
}

$location includes the URL fragment, which is stored with no encoding — MediaObjectTrait::urlHash() L240-249 only strips a leading #. Before that, the excerpt handler decodes the media URL with htmlspecialchars_decode(urldecode(...)), undoing Parsedown's escaping — Excerpts.php L188 — and routes the fragment to urlHash() at Excerpts.php L321-323. So ", <, >, =, (, ) in the fragment survive into the raw <source>.

Two defenses that stop the querystring path do not cover the fragment:

• The GFM tagfilter — ParsedownGravTrait::filterDisallowedRawHtml() L528-535 — escapes < only for title|textarea|style|xmp|iframe|noembed|noframes|script|plaintext. <svg> and <img> are not on the list, so they inject as live markup.
• The __call querystring passthrough rawurlencodes its values, but the fragment…

Duplicate Advisory

This advisory has been withdrawn because it is a duplicate of GHSA-6qw9-4vv5-jr97. This link is maintained to preserve external references.

Original Description

Grav before 2.0.15 contains a stored cross-site scripting vulnerability in the audio and video media rendering through the sourceParsedownElement method. The media URL fragment is concatenated unescaped into rawHtml source elements, allowing attackers to inject arbitrary HTML and JavaScript that executes in viewers' sessions.

Grav before 2.0.15 contains a stored cross-site scripting vulnerability in the audio and video media rendering through the sourceParsedownElement method. The media URL fragment is concatenated unescaped into rawHtml source elements, allowing attackers to inject arbitrary HTML and JavaScript that executes in viewers' sessions.

Grav before 2.0.15 contains a stored cross-site scripting vulnerability in the audio and video media rendering through the sourceParsedownElement method. The media URL fragment is concatenated unescaped into rawHtml source elements, allowing attackers to inject arbitrary HTML and JavaScript that executes in viewers' sessions.

Target: github.com/getgrav/grav
Affected resource: Grav\Common\Media\Traits\AudioMediaTrait / VideoMediaTrait sourceParsedownElement() — verified on 2.0.13 (latest stable) and develop HEAD 5a7070f
Severity: Medium (~6.9 CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:L/A:N — anchored to the sibling script-XSS advisory CVE-2026-42841, same PR:H / S:C / C:H / I:L)
Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

Summary

A Markdown audio or video embed renders its <source> element as raw HTML with the media URL concatenated unescaped. The URL fragment is reflected without any encoding, so ![x](song.mp3#"><svg/onload=alert(1)>) breaks out of <source src="…"> and injects arbitrary HTML — including a script-executing <svg onload> — into the rendered page. Any user who views the page runs the attacker's JavaScript in their session; a logged-in administrator who views it exposes their same-origin Grav Admin session to the attacker's script.

This is the next sink in the media-parameter injection class the maintainer has been closing: GHSA-r7fx-8g49-7hhr (attribute()), GHSA-pmf8-g7c8-7v54 / CVE-2026-55890 (style(), 2.0.0-rc.9), and GHSA-ffmg-hfvg-jhg9 (resize(), 2.0.0-rc.10). All three guarded image style/attribute sinks; the aba291a5 audit scoped itself to "sinks reaching the style attribute" and did not cover the audio/video <source> rawHtml sink, which reaches full script execution rather than CSS injection.

Root Cause

The audio/video player builds its inner source as Parsedown rawHtml (emitted verbatim, unescaped), concatenating the media URL directly into a double-quoted attribute — AudioMediaTrait.php L43-52 (identical in VideoMediaTrait.php L58-67):

protected function sourceParsedownElement(array $attributes, $reset = true)
{
    $location = $this->url($reset);
    return [
        'name' => 'audio',
        'rawHtml' => '<source src="' . $location . '">Your browser does not support the audio tag.',
        'attributes' => $attributes
    ];
}

$location includes the URL fragment, which is stored with no encoding — MediaObjectTrait::urlHash() L240-249 only strips a leading #. Before that, the excerpt handler decodes the media URL with htmlspecialchars_decode(urldecode(...)), undoing Parsedown's escaping — Excerpts.php L188 — and routes the fragment to urlHash() at Excerpts.php L321-323. So ", <, >, =, (, ) in the fragment survive into the raw <source>.

Two defenses that stop the querystring path do not cover the fragment:

• The GFM tagfilter — ParsedownGravTrait::filterDisallowedRawHtml() L528-535 — escapes < only for title|textarea|style|xmp|iframe|noembed|noframes|script|plaintext. <svg> and <img> are not on the list, so they inject as live markup.
• The __call querystring passthrough rawurlencodes its values, but the fragment…

Duplicate Advisory

This advisory has been withdrawn because it is a duplicate of GHSA-6qw9-4vv5-jr97. This link is maintained to preserve external references.

Original Description

Grav before 2.0.15 contains a stored cross-site scripting vulnerability in the audio and video media rendering through the sourceParsedownElement method. The media URL fragment is concatenated unescaped into rawHtml source elements, allowing attackers to inject arbitrary HTML and JavaScript that executes in viewers' sessions.