GHSA-9rcc-pmj8-ffhr

### Summary

Special:FacetedSearch `cstate` hidden inputs enable reflected XSS (residual of CVE-2025-10354)

### Details

#### Affected versions and vulnerable location

- Confirmed present on latest shipped release tag available in the local clone: `SemanticMediaWiki/SemanticMediaWiki@7.2.0`. - Confirmed present on default branch `master` at HEAD `18f418b4cdf2875e67a741349179a22c1573f61c`.

Vulnerable sink (default-branch representation):

- `src/MediaWiki/Specials/FacetedSearch/HtmlBuilder.php:131-133` - Builds `$hidden` by concatenating unescaped request-controlled `cstate[$key]` values into an HTML attribute context (`value="..."`). - `templates/FacetedSearch/search.mustache:25` - Inserts the constructed fragment via `{{{hidden}}}` (no HTML escaping at this boundary).

#### Reachability trace (verified from source)

1. HTTP entrypoint: - `GET` to `Special:FacetedSearch` dispatches into `SMW\MediaWiki\Specials\SpecialFacetedSearch::execute()`. 2. Request decoding boundary: - `SpecialFacetedSearch::execute()` constructs `UrlArgs` from `$request->getValues()` and calls `ParametersProcessor::checkRequest($request)`. 3. Checksum gate: - `ParametersProcessor::checkRequest()` clears `cstate` only when `filtered != 1` and `getInt('csum', 0) != crc32(getVal('q', ''))`. 4. Decoder -> HTML assembly: - `HtmlBuilder::buildHTML()` iterates `foreach ( $urlArgs->getArray( 'cstate' ) as $key => $value )` and concatenates each into `$hidden` without escaping. - `HtmlBuilder::buildHTML()` passes `$hidden` into the template variable `hidden`. 5. HTML injection sink: - `templates/FacetedSearch/search.mustache` renders `{{{hidden}}}` into the `<form>`, so the concatenated markup is inserted as raw HTML.

### PoC

#### Reproduction steps (source-derived)

1. Choose a `q` value. 2. Compute `csum` as `crc32(q)`. 3. Send a request that includes: - `q=<chosen>` - `csum=<crc32(q)>` - at least one `cstate[<key>]=<payload>` entry

Example request shape:

```text /index.php/Special:FacetedSearch?q=Text&csum=<crc32(Text)>&cstate[0]=x%22%20autofocus%20onfocus%3Dalert(1)%20x%22 ```

### Impact

#### Attacker model

- Any remote attacker who can send HTTP requests to `Special:FacetedSearch` (or the localized alias mapped to the same `SpecialFacetedSearch` class) can supply attacker-controlled query parameters. - Preconditions: - The attacker must make `cstate` survive `ParametersProcessor::checkRequest()`, either by setting `csum` to `crc32(q)` (when `filtered != 1`), or by setting `filtered=1`. - The attacker must supply `cstate[<key>]` values containing characters that break out of the HTML `value="..."` attribute context (for example an injected `"` to terminate the attribute value).

#### Severity and CVSS reasoning

Proposed severity: MEDIUM.

Proposed CVSS v3.1 vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`.

Rationale:

- AV:N: delivered over the network via query parameters. - AC:L: requires only setting `q`, `csum`, and at least one `cstate` entry. - PR:N: no authentication required for the request path in this code. - UI:R: the victim must load the crafted URL. - S:C: reflected XSS executes in the wiki origin and can affect other users depending on deployment and browser behavior.

### Why this is a residual of CVE-2025-10354

- The CVE-2025-10354 hardening shipped by escaping the `q` parameter before emitting it into the `value="{{q}}"` attribute. - Commit `3d675ce` updates only the `q` rendering to use `htmlspecialchars( $urlArgs->get( 'q', '' ) )` and does not touch the adjacent `cstate` -> `$hidden` construction loop. - As a result, `cstate` remains an unescaped input source that flows into the same raw template injection point (`{{{hidden}}}`), creating a distinct reflected-XSS lane.

### Output (from code inspection)

Given the payload idea where `cstate[0]` starts with `x" ... x"`, `HtmlBuilder.php` constructs the hidden fragment by concatenation:

```html <input name="cstate[0]" type="hidden" value="x" autofocus onfocus=alert(1) x"> ```

Because `search.mustache` injects the fragment via `{{{hidden}}}`, the attacker-controlled markup participates in normal HTML parsing in the response body.

### Suggested fix

- Escape both the `cstate` key and value when constructing `$hidden`. - Minimal code change in `src/MediaWiki/Specials/FacetedSearch/HtmlBuilder.php`:

```php foreach ( $urlArgs->getArray( 'cstate' ) as $key => $value ) { $safeKey = htmlspecialchars( (string)$key, ENT_QUOTES, 'UTF-8' ); $safeValue = htmlspecialchars( (string)$value, ENT_QUOTES, 'UTF-8' ); $hidden .= '<input name="cstate[' . $safeKey . ']" type="hidden" value="' . $safeValue . '">'; } ```

This keeps the raw `{{{hidden}}}` template insertion safe by ensuring the concatenated HTML fragment itself is attribute-escaped.

### How I found it and a note on tooling

I anchored on the published CVE-2025-10354 patch by verifying in the checked-out repository that commit `3d675ce` changes only the `q` rendering in `HtmlBuilder.php` to use `htmlspecialchars`.

Then I traced the reachable request path from `SpecialFacetedSearch::execute()` through `ParametersProcessor::checkRequest()` (checksum gate for whether `cstate` survives) into `HtmlBuilder::buildHTML()` where `$hidden` is constructed from `cstate` without escaping and injected into `templates/FacetedSearch/search.mustache` via `{{{hidden}}}`.

(End of file)

### AI tooling

I used AI assistance for the code audit and for drafting this report. I manually verified the finding against the project's source at the location cited above before reporting it, and the severity and impact assessment are my own.