Koa is expressive middleware for Node.js using ES2017 async functions. Prior to versions 0.21.2, 1.7.1, 2.15.4, and 3.0.0-alpha.3, Koa uses an evil regex to parse the X-Forwarded-Proto and X-Forwarded-Host HTTP headers. This can be exploited to carry out a Denial-of-Service attack. Versions 0.21.2, 1.7.1, 2.15.4, and 3.0.0-alpha.3 fix the issue.
Weakness
The product uses a regular expression with an inefficient, possibly exponential worst-case computational complexity that consumes excessive CPU cycles.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Koa | Koajs | * | 0.21.2 (excluding) |
| Koa | Koajs | 1.0.0 (including) | 1.7.1 (excluding) |
| Koa | Koajs | 2.0.0 (including) | 2.15.4 (excluding) |
| Koa | Koajs | 3.0.0-alpha0 (including) | 3.0.0-alpha0 (including) |
| Koa | Koajs | 3.0.0-alpha1 (including) | 3.0.0-alpha1 (including) |
| Koa | Koajs | 3.0.0-alpha2 (including) | 3.0.0-alpha2 (including) |
Extended Description
Attackers can create crafted inputs that
intentionally cause the regular expression to use
excessive backtracking in a way that causes the CPU
consumption to spike.
Potential Mitigations
Related Attack Patterns
References
- https://github.com/koajs/koa/blob/master/lib/request.js#L259
- https://github.com/koajs/koa/blob/master/lib/request.js#L404
- https://github.com/koajs/koa/commit/5054af6e31ffd451a4151a1fe144cef6e5d0d83c
- https://github.com/koajs/koa/commit/5f294bb1c7c8d9c61904378d250439a321bffd32
- https://github.com/koajs/koa/commit/93fe903fc966635a991bcf890cfc3427d33a1a08
- https://github.com/koajs/koa/releases/tag/2.15.4
- https://github.com/koajs/koa/security/advisories/GHSA-593f-38f6-jp5m