CVE-2023-20057 - Bypassing URL Reputation Filters in Cisco AsyncOS Software for Cisco Email Security Appliance (ESA)

A newly discovered vulnerability within Cisco's AsyncOS Software for Cisco Email Security Appliance (ESA) allows unauthenticated, remote attackers to bypass the crucial URL reputation filters. Assigned with the CVE identifier CVE-2023-20057, this vulnerability stems from the software's improper handling and processing of URLs. Successful exploitation could result in malicious URLs passing through the device, potentially leading to more significant security threats. This long-read post will provide further insight into the exploit details, including code snippets and how to address this vulnerability effectively.

Exploit details

The core issue with Cisco AsyncOS Software lies in the mishandling of URL processing. When an attacker crafts a specially formatted URL, the software fails to recognize it as malicious, allowing it to bypass the configured URL reputation filters on the ESA device. Consequently, this provides an opportunity for potential cyber threats and compromises the overall security of the system.

Here's an example of a crafted URL that might exploit this vulnerability

http://malicious.example.com/bypass[@]safe.example.com

In the crafted URL above, the '@' symbol is used to trick the filters into reading the URL as safe.example.com instead of malicious.example.com.

Original references

1. The official Cisco advisory detailing this vulnerability comprehensively can be accessed at Cisco Advisory AsyncOS URL Filtering Vulnerability

2. The CVE reference for this vulnerability can be found at the following link: CVE-2023-20057

Mitigation and suggested actions

Cisco has released software updates addressing this vulnerability for affected devices. It is strongly recommended that users update their devices to the latest software versions as soon as possible to prevent potential exploits.

Cisco provides detailed steps and guidelines for upgrading AsyncOS on ESA devices in their guide: Upgrading AsyncOS on Cisco Email Security Appliances

Additionally, ensure that your device has the latest URL filtering engine updates by periodically checking for new updates.

Conclusion

The CVE-2023-20057 vulnerability exposes Cisco Email Security Appliance (ESA) devices to potential threats by allowing the bypass of URL reputation filters. This long-read post has provided insight into the exploit details while shedding light on the recommended mitigation strategies. By being proactive and implementing the suggested actions, you will ensure that your system maintains the necessary security levels and minimizes the chances of a successful attack.

Timeline

Published on: 01/20/2023 07:15:00 UTC
Last modified on: 03/01/2023 08:15:00 UTC