Gogs is an open source self-hosted Git service. Prior to 0.14.3, specially crafted issue index pattern can cause a panic when rendering, resulting in denial of service. In internal/markup/markup.go, RenderIssueIndexPattern renders the issue index pattern to a link using com.Expand, which is not safe: when the configured pattern contains an opening brace { but no closing brace }, strings.Index(template, "}") returns -1 and the subsequent slice template[:-1] triggers a panic. Once such a pattern is set, any page in the affected repository that contains an issue index reference such as #1 becomes unavailable. This vulnerability is fixed in 0.14.3.

Affected: Go: gogs.io/gogs

### Summary Special template of issue index pattern may cause panic.

### Details

in internal/markup/markup.go

```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.

```go 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


finally, all pages than contains issue index are unavailable.

### PoC

1. set issue index pattern as follow


2. add a commit which point to an issue in its msg


using `#1` above

### Impact

DoS that cause part of pages of the specify repo unavailable.

Ein Angreifer kann mehrere Schwachstellen in Gogs ausnutzen, um erweiterte Berechtigungen zu erlangen, beliebigen Code auszuführen – sogar mit erweiterten Berechtigungen, was zur vollständigen Kontrolle über das System führen kann –, Sicherheitsmaßnahmen zu umgehen, Daten zu manipulieren, Cross-Site-Scripting-Angriffe durchzuführen, Benutzer auf bösartige Websites umzuleiten oder einen Denial-of-Service-Zustand zu verursachen.