High · published December 5, 2025
⚡ This sneaky flaw in urllib3 allows a crafty server to send you a never-ending compression chain—think of it as an onion that just keeps adding layers! 🧅 Imagine a mailroom that keeps receiving parcels, but each parcel contains instructions for sending even more parcels—before you know it, the whole place is overflowing! That’s what happens with the unbounded decompression chain; it leads to high CPU usage and massive memory allocation that could freeze your application. An attacker can overwhelm your application by exploiting this vulnerability, leading to potential denial of service due to excessive resource consumption. This means your server could slow to a crawl or even crash under the weight of endless compressed data, leaving your users hanging!
Imagine a mailroom that keeps receiving parcels, but each parcel contains instructions for sending even more parcels—before you know it, the whole place is overflowing! That’s what happens with the unbounded decompression chain; it leads to high CPU usage and massive memory allocation that could freeze your application. This vulnerability allows a malicious server to exploit urllib3 by sending a limitless number of compression steps, which leads to catastrophic CPU and memory strain on the client. Affected versions include 1.24 through 2.6.0, which are susceptible to this issue.
An attacker can overwhelm your application by exploiting this vulnerability, leading to potential denial of service due to excessive resource consumption. This means your server could slow to a crawl or even crash under the weight of endless compressed data, leaving your users hanging! Upgrade urllib3 to version 2.6.0 immediately to patch this vulnerability. Also, consider implementing resource limits to mitigate potential abuse in the future. Don't let your application fall victim to this sneaky issue! You've got this! By following these steps, you're on your way to securing your application like a pro! 🛡️
| Product | Versions | Fixed in |
|---|---|---|
| python/urllib3 | ≥ 1.24, < 2.6.0 | 2.6.0 |