Swift Prometheus is a Swift client for the Prometheus monitoring system, supporting counters, gauges and histograms. In code which applies _un-sanitized string values into metric names or labels_, an attacker could make use of this and send a `?lang` query parameter containing newlines, `}` or similar characters which can lead to the attacker taking over the exported format -- including creating unbounded numbers of stored metrics, inflating server memory usage, or causing "bogus" metrics. This vulnerability is fixed in2.0.0-alpha.2.
Affected: SwiftURL: github.com/swift-server/swift-prometheus
### Impact
In code which applies _un-sanitized string values into metric names or labels_, like this:
```swift let lang = try? request.query-get(String.self, at: "lang") Counter ( label: "language", dimensions: [("lang", lang ?? "unknown" )] ) ```
an attacker could make use of this and send a `?lang` query parameter containing newlines, `}` or similar characters which can lead to the attacker taking over the exported format -- including creating unbounded numbers of stored metrics, inflating server memory usage, or causing "bogus" metrics.
### Patches The default strategy to sanitize labels was moved deeper into the library, preventing illegal characters from appearing in name, label keys and values.
Metric names and label names are now validated against the following requirement: `[a-zA-Z_:][a-zA-Z0-9_:]*` (for metric names) and `[a-zA-Z_][a-zA-Z0-9_]*` (for metric label names). Label values are not validated as they are allowed to contain any unicode characters. Developers _must_ validate labels themselves and not allow malicious input.
The approach taken here mirrors the approach taken in the Go reference implementation.
### Discussion
It is **strongly discouraged** to use un-sanitized user input as names or labels in general, because they can lead to un-bounded growth of metrics, even as this vulnerability is patched and result in a Denial-of-Service attack opportunity -- **regardless** how well the library is sanitizing the inputs. We strongly recommend on…