SillyTavern is a locally installed user interface that allows users to interact with text generation large language models, image generation engines, and text-to-speech voice models. Prior to 1.18.0, when fetch(url) throws, the code sends:
res.status(500).send('Error occurred while trying to proxy to: ' + url + ' ' + error). The url value is attacker-controlled (req.params.url) and is not HTML-escaped before rendering. This vulnerability is fixed in 1.18.0.