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Validate Accept-Language header in HeaderLanguageProvider #5

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Merged
alexstandiford merged 1 commit into from
Jun 11, 2026
Merged

Validate Accept-Language header in HeaderLanguageProvider #5

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16 changes: 10 additions & 6 deletions lib/Providers/HeaderLanguageProvider.php
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Original file line number Diff line number Diff line change
Expand Up @@ -11,14 +11,18 @@ class HeaderLanguageProvider
*/
public function getLanguage(): ?string
{
if (isset($_SERVER['HTTP_ACCEPT_LANGUAGE'])) {
$languages = explode(',', $_SERVER['HTTP_ACCEPT_LANGUAGE']);
if (!isset($_SERVER['HTTP_ACCEPT_LANGUAGE']) || !is_string($_SERVER['HTTP_ACCEPT_LANGUAGE'])) {
return null;
}

// The header is attacker-controlled: validate the primary entry
// against the language-tag shape instead of trusting raw bytes.
$primary = explode(',', $_SERVER['HTTP_ACCEPT_LANGUAGE'])[0];

if (!empty($languages[0])) {
return strtolower(substr($languages[0], 0, 2));
}
if (!preg_match('/^\s*([a-zA-Z]{2})(?:[-_][a-zA-Z0-9]{2,8})*\s*(?:;.*)?$/', $primary, $matches)) {
return null;
}

return null;
return strtolower($matches[1]);
}
}
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