Western Alliance Bank has alerted nearly 22,000 customers that their personal information was compromised following a cyberattack in October. The breach stemmed from a vulnerability in a third-party vendor’s secure file transfer software, which allowed attackers to gain unauthorized access to the bank’s systems and extract sensitive customer data. 

Western Alliance, a subsidiary of Western Alliance Bancorporation with over $80 billion in assets, first disclosed the incident in a February SEC filing. The bank revealed that hackers exploited a zero-day vulnerability in the software, which was officially disclosed on October 27, 2024. However, unauthorized access to the bank’s systems had already occurred between October 12 and October 24. The breach was only confirmed after the attackers leaked stolen files online. 

According to breach notification letters sent to 21,899 affected customers and filed with the Office of Maine’s Attorney General, the stolen data includes names, Social Security numbers, birth dates, financial account details, driver’s license numbers, tax identification numbers, and passport information if previously provided to the bank. Despite the exposure, Western Alliance stated there is no evidence of fraud or identity theft resulting from the breach. 

To support affected customers, the bank is offering one year of free identity protection services through Experian IdentityWorks Credit 3B. Although Western Alliance did not disclose the name of the compromised software in its SEC filing or customer notifications, the Clop ransomware gang has claimed responsibility for the attack. In January, Clop listed the bank among 58 companies targeted in a campaign that exploited a critical zero-day vulnerability (CVE-2024-50623) in Cleo LexiCom, VLTransfer, and Harmony software. 

The ransomware group had previously leveraged similar security flaws in MOVEit Transfer, GoAnywhere MFT, and Accellion FTA to conduct large-scale data theft operations. Further investigations revealed that Clop exploited an additional zero-day vulnerability (CVE-2024-55956) in Cleo software in December. This allowed them to deploy a Java-based backdoor, dubbed “Malichus,” enabling deeper infiltration into victims’ networks. Cleo, which serves over 4,000 organizations worldwide, confirmed the vulnerability had been used to install malicious backdoor code in affected instances of its Harmony, VLTrader, and LexiCom software. 

The full extent of the breach remains unclear, but it highlights the growing risks posed by vulnerabilities in third-party software. Organizations relying on such solutions must remain vigilant, promptly apply security patches, and implement robust defenses to prevent similar incidents.