GHSA-4j89-2c4f-44c6: Gogs has DoS in rendering issue index pattern

Summary Special template of issue index pattern may cause panic. Details in internal/markup/markup.go link = fmt.Sprintf(<a href="%s">%s</a>, com.Expand(metas["format"], metas), m) Issue index pattern is rendered to link with com.Expand. However, com.Expand is not safe. i = strings.Index(template, "}") if s, ok := match[template[:i]]; ok { when { is found but } not found, i comes to 1, template[:-1] will be called, and then panicked image finally, all pages than contains issue index are unavailable. PoC 1. set issue index pattern as follow image 2. add a commit which point to an issue in its msg image using #1 above Impact DoS that cause part of pages of the specify repo unavailable.