GHSA-rhj7-vh3v-mcq6 - Daptin: ParseAcceptLanguage `_` separator bypass enables >250x CPU amplification via Accept-Language header in LanguageMiddleware

### Summary Daptin's `LanguageMiddleware` (registered as a global gin middleware) calls `golang.org/x/text/language.ParseAcceptLanguage` on the raw `Accept-Language` header of every HTTP request without imposing any size or shape filter. The underlying parser has quadratic-time behaviour on long lists of malformed language tags. The CVE-2022-32149 guard that golang.org/x/text added in v0.3.8 caps the number of `-` characters in the input at 1000, but it does not cap `_` characters even though the parser's internal scanner aliases `_` to `-` before parsing. A single unauthenticated GET request with an `Accept-Language` header built out of `_` separators (only 256 KiB, not even the 1 MiB ceiling) consumes about 27 seconds of server CPU on the host running Daptin. A 1 MiB payload exceeds the 2-minute test client timeout. A single attacker on a 1 Mbit/s uplink can pin an entire Daptin host with one request every 30 seconds. ### Affected versions `github.com/daptin/daptin` v0.12.15 and (per code inspection of `master`) all earlier 0.12.x versions that wire `LanguageMiddleware` on the global gin router without imposing their own size limit on `Accept-Language`. Verified on: - the official release binary `daptin-linux-amd64` v0.12.15 built into a Docker image from the project's own `Dockerfile` (E2E below) - `master` at commit `b021ac4ae1f72b7401e851fcf883bc970303c794` by reading `server/language.go` (the middleware is unchanged) ### Privilege required Unauthenticated. The middleware is registered on the global gin router that serves both the public landing page and the unauthenticated `/api` style endpoints. Anyone who can reach the HTTP listener (port 8080 by default) is in scope. ### Vulnerable code [`server/language.go`](https://github.com/daptin/daptin/blob/b021ac4ae1f72b7401e851fcf883bc970303c794/server/language.go) (blob SHA `b021ac4ae1f72b7401e851fcf883bc970303c794`): ```go func (lm *LanguageMiddleware) LanguageMiddlewareFunc(c *gin.Context) { pref :=