A critical vulnerability tracked as CVE-2024-20439 has placed Cisco’s Smart Licensing Utility (CSLU) in the spotlight after cybersecurity researchers observed active exploitation attempts. The flaw, which involves an undocumented static administrative credential, could allow unauthenticated attackers to remotely access affected systems. While it’s still unclear whether the vulnerability has been weaponized in ransomware attacks, security experts have noted suspicious botnet activity linked to it since early January, with a significant surge in mid-March.
The vulnerability, according to Cisco, cannot be exploited unless the CSLU is actively running—a saving grace for systems not using the utility frequently. However, many organizations rely on the CSLU to manage licenses for Cisco products without requiring constant connectivity to Cisco’s cloud-based Smart Software Manager. This increases the risk of exposure for unpatched systems.
Johannes Ullrich, Dean of Research at the SANS Technology Institute, highlighted that the vulnerability effectively acts as a backdoor.
In fact, he noted that Cisco has a history of embedding static credentials in several of its products. Ullrich’s observation aligns with earlier research by Nicholas Starke, who published a detailed technical analysis of the flaw, including the decoded hardcoded password, just weeks after Cisco issued its patch. This disclosure made it easier for potential attackers to identify and exploit vulnerable systems.
In addition to CVE-2024-20439, Cisco addressed another critical flaw, CVE-2024-20440, which allows unauthenticated attackers to extract sensitive data from exposed devices, including API credentials.
This vulnerability also affects the CSLU and can be exploited by sending specially crafted HTTP requests to a target system. Like the first flaw, it is only active when the CSLU application is running.
Researchers have now detected attackers chaining both vulnerabilities to maximize impact. According to Ullrich, scans and probes originating from a small botnet are testing for exposure to these flaws. Although Cisco’s Product Security Incident Response Team (PSIRT) maintains that there’s no confirmed evidence of these flaws being exploited in the wild, the published credentials and recent scan activity suggest otherwise.
These types of vulnerabilities raise larger concerns about the use of hardcoded credentials in critical infrastructure. Cisco has faced similar issues in the past with other software products, including IOS XE, DNA Center, and Emergency Responder.
As always, the best defense is prompt patching. Cisco released security updates in September to address both flaws, and organizations running CSLU should immediately apply them. Additionally, any instance of the CSLU running unnecessarily should be disabled to reduce the attack surface. With exploit attempts on the rise and technical details now public, delaying mitigation could have serious consequences.