AdonisJS HTTP Server is a package for handling HTTP requests in the AdonisJS framework. Prior to 8.2.2 and 9.1.1, the regular expression returned by router.matchers.slug() contains adjacent greedy repetitions with overlapping character classes. When an application applies this matcher to an attacker-controlled route parameter, a long slug ending in a character rejected by the final assertion causes quadratic backtracking and excessive CPU use. Route matching occurs before route and group middleware, so authentication or rate-limiting middleware attached to the route may not prevent an unauthenticated request from blocking the Node.js event loop and stopping the worker from serving unrelated requests or health checks. This issue is fixed in versions 8.2.2 and 9.1.1.

Affected: npm: @adonisjs/http-server

### Description

A Regular Expression Denial of Service vulnerability in the built-in AdonisJS slug route matcher may allow a remote attacker to block the Node.js event loop using a specially crafted URL.

This affects applications using `router.matchers.slug()` on a route parameter reachable by an attacker.

### Details

The regular expression used by `router.matchers.slug()` contains adjacent greedy quantifiers with overlapping character classes:

```regex /^[^\s-_](?!.*?[-_]{2,})([a-z0-9-\\]{1,})[^\s]*[^-_\s]$/ ```

When the matcher receives a long string ending with a character rejected by the final assertion, the regular expression engine must evaluate many possible ways of dividing the input between the overlapping quantifiers before determining that it does not match.

This results in quadratic execution time. Testing measured an approximate complexity of `O(n^1.98)`.

Route matchers are evaluated against attacker-controlled URL segments during routing. Therefore, an unauthenticated attacker can trigger the vulnerable expression by sending a request to a route configured as follows:

```ts router .get('/posts/:slug', handler) .where('slug', router.matchers.slug()) ```

Routing occurs before route and group middleware. As a result, authentication or rate-limiting middleware attached to the affected route may not prevent exploitation.

The vulnerability is limited to routes that explicitly use the built-in slug matcher.

### Impact

Exploitation requires an applicat…