ffcss is a CLI interface to apply and configure Firefox CSS themes. Prior to 0.2.0, the function `lookupPreprocess()` is meant to apply some transformations to a string by disabling characters in the regex `[-_ .]`. However, due to the use of late Unicode normalization of type NFKD, it is possible to bypass that validation and re-introduce all the characters in the regex `[-_ .]`. The `lookupPreprocess()` can be easily bypassed with equivalent Unicode characters like U+FE4D (﹍), which would result in the omitted U+005F (_), for instance. The `lookupPreprocess()` function is only ever used to search for themes loosely (case insensitively, while ignoring dashes, underscores and dots), so the actual security impact is classified as low. This vulnerability is fixed in 0.2.0. There are no known workarounds.

Affected: Go: github.com/ewen-lbh/ffcss

### Summary The function `lookupPreprocess()` is meant to apply some transformations to a string by disabling characters in the regex `[-_ .]`. However, due to the use of late Unicode normalization of type NFKD, it is possible to bypass that validation and re-introduce all the characters in the regex `[-_ .]`.

```go // lookupPreprocess applies transformations to s so that it can be compared // to search for something. // For example, it is used by (ThemeStore).Lookup func lookupPreprocess(s string) string { return strings.ToLower(norm.NFKD.String(regexp.MustCompile(`[-_ .]`).ReplaceAllString(s, ""))) } ```

Take the following equivalent Unicode character U+2024 (․). Initially, the `lookupPreprocess()` function would compile the regex and replace the regular dot (.). However, the U+2024 (․) would bypass the `ReplaceAllString()`. When the normalization operation is applied to U+2024 (․), the resulting character will be U+002E (.). Thus, the dot was reintroduced back.

### Impact

The `lookupPreprocess()` can be easily bypassed with equivalent Unicode characters like U+FE4D (﹍), which would result in the omitted U+005F (_), for instance. It should be noted here that the variable `s` is user-controlled data coming from [/cmd/ffcss/commands.go#L22-L28](https://github.com/ewen-lbh/ffcss/blob/master/cmd/ffcss/commands.go#L22-L28) the command args. The `lookupPreprocess()` function is only ever used to search for themes loosely (case insensitively, while ignoring dashes, undersc…