CVE-2020-5236 Explained : Impact and Mitigation
Learn about CVE-2020-5236, a vulnerability in Waitress version 1.4.2 allowing a DOS attack due to catastrophic backtracking in regex. Find mitigation steps and upgrade recommendations here.
Waitress version 1.4.2 allows a DOS attack when receiving headers with invalid characters, causing CPU usage to spike and blocking interactions.
Understanding CVE-2020-5236
What is CVE-2020-5236?
Waitress version 1.4.2 is vulnerable to a Denial of Service (DOS) attack due to catastrophic backtracking in regex when processing headers with invalid characters.
The Impact of CVE-2020-5236
This vulnerability allows an attacker to send a single request with an invalid header, leading to a 100% CPU usage spike and service unavailability.
Technical Details of CVE-2020-5236
Vulnerability Description
- Waitress version 1.4.2 experiences catastrophic backtracking in regex when processing headers with invalid characters.
Affected Systems and Versions
- Product: Waitress
- Vendor: Pylons
- Affected Version: 1.4.2
Exploitation Mechanism
- Sending a header like "Bad-header: xxxxxxxxxxxxxxx\x10" triggers the regex engine to backtrack, causing high CPU usage and service blockage.
Mitigation and Prevention
Immediate Steps to Take
- Upgrade to Waitress version 1.4.3 where the regex for validating headers has been updated.
Long-Term Security Practices
- Regularly update software to the latest versions to patch vulnerabilities.
Patching and Updates
- It is recommended to upgrade to Waitress version 1.4.3 to mitigate the DOS vulnerability.