Incident Score: Analysis & Impact (MAI1781188499)
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Rankiteo Score Impact Analysis
Key Highlights From The Incident Analysis
- Timeline of Mainstreet Credit Union's Breach and lateral movement inside company's environment.
- Overview of affected data sets, including SSNs and PHI, and why they materially increase incident severity.
- How Rankiteo’s incident engine converts technical details into a normalized incident score.
- How this cyber incident impacts Mainstreet Credit Union Rankiteo cyber scoring and cyber rating.
- Rankiteo’s MITRE ATT&CK correlation analysis for this incident, with associated confidence level.
Full Incident Analysis Transcript
In this Rankiteo incident briefing, we review the Mainstreet Credit Union breach identified under incident ID MAI1781188499.
The analysis begins with a detailed overview of Mainstreet Credit Union's information like the linkedin page: https://www.linkedin.com/company/mainstreet-credit-union, the number of followers: 1048, the industry type: Banking and the number of employees: 114 employees
After the initial compromise, the video explains how Rankiteo's incident engine converts technical details into a normalized incident score. The incident score before the incident was 754 and after the incident was 669 with a difference of -85 which is could be a good indicator of the severity and impact of the incident.
In the next step of the video, we will analyze in more details the incident and the impact it had on Mainstreet Credit Union and their customers.
On 04 May 2026, Mainstreet Credit Union disclosed Data Breach issues under the banner "Mainstreet Credit Union Data Breach".
Mainstreet Credit Union reported a data breach impacting 4,123 individuals across the U.S.
The disruption is felt across the environment, affecting Microsoft 365 email account, and exposing Sensitive personal data including Social Security numbers, names, financial account details, and driver's license numbers, with nearly 4123 records at risk.
In response, teams activated the incident response plan, moved swiftly to contain the threat with measures like Secured the compromised email account, and began remediation that includes Engaged forensic investigation, provided identity monitoring services, and stakeholders are being briefed through Notified affected individuals and Indiana Attorney General, established dedicated support line.
The case underscores how Completed, with advisories going out to stakeholders covering Provided 12 months of complimentary identity monitoring through Kroll, established dedicated support line (844-403-4628).
Finally, we try to match the incident with the MITRE ATT&CK framework to see if there is any correlation between the incident and the MITRE ATT&CK framework.
The MITRE ATT&CK framework is a knowledge base of techniques and sub-techniques that are used to describe the tactics and procedures of cyber adversaries. It is a powerful tool for understanding the threat landscape and for developing effective defense strategies.
MITRE ATT&CK® Correlation Analysis
Rankiteo's analysis has identified several MITRE ATT&CK tactics and techniques associated with this incident, each with varying levels of confidence based on available evidence. Under the Initial Access tactic, the analysis identified Phishing: Spearphishing Link (T1566.002) with moderate to high confidence (80%), with evidence including suspicious activity in an employee’s email account, and compromised Microsoft 365 email account and Valid Accounts: Cloud Accounts (T1078.004) with high confidence (90%), supported by evidence indicating unauthorized actor accessed the Microsoft 365 email account. Under the Credential Access tactic, the analysis identified Email Collection: Remote Email Collection (T1114.002) with moderate to high confidence (80%), supported by evidence indicating exact emails and attachments viewed could not be determined and Unsecured Credentials: Cloud Credentials (T1552.006) with moderate to high confidence (70%), supported by evidence indicating compromised Microsoft 365 email account. Under the Collection tactic, the analysis identified Email Collection: Remote Email Collection (T1114.002) with high confidence (90%), supported by evidence indicating sensitive personal data...was exposed via email account and Data from Information Repositories: Sharepoint (T1213.002) with moderate confidence (60%), supported by evidence indicating microsoft 365 email account compromised (implies cloud data access). Under the Exfiltration tactic, the analysis identified Exfiltration Over C2 Channel (T1041) with moderate to high confidence (70%), supported by evidence indicating data breach impacting 4,123 individuals and Transfer Data to Cloud Account (T1537) with moderate confidence (60%), supported by evidence indicating unauthorized actor accessed Microsoft 365 email account. Under the Impact tactic, the analysis identified Data Destruction (T1485) with lower confidence (30%), supported by evidence indicating no details on data destruction, but sensitive data exposed and Data Manipulation: Transmitted Data Manipulation (T1565.002) with lower confidence (40%), supported by evidence indicating unauthorized access to email account (potential tampering). Under the Defense Evasion tactic, the analysis identified Hide Artifacts: Email Hiding Rules (T1564.008) with moderate confidence (60%), supported by evidence indicating exact emails and attachments viewed could not be determined and Valid Accounts: Cloud Accounts (T1078.004) with moderate to high confidence (70%), supported by evidence indicating unauthorized actor accessed Microsoft 365 email account. These correlations help security teams understand the attack chain and develop appropriate defensive measures based on the observed tactics and techniques.
Sources & References
- Mainstreet Credit Union Rankiteo Cyber Incident Details: https://www.rankiteo.com/company/mainstreet-credit-union/incident/MAI1781188499
- Mainstreet Credit Union CyberSecurity Rating page: https://www.rankiteo.com/company/mainstreet-credit-union
- Mainstreet Credit Union Rankiteo Cyber Incident Blog Article: https://blog.rankiteo.com/mai1781188499-mainstreet-credit-union-breach-may-2026/
- Mainstreet Credit Union CyberSecurity Score History: https://www.rankiteo.com/company/mainstreet-credit-union/history
- Mainstreet Credit Union CyberSecurity Incident Source: https://www.claimdepot.com/data-breach/mainstreet-credit-union-2026
- Rankiteo A.I CyberSecurity Rating methodology: https://www.rankiteo.com/Images/rankiteo_algo.pdf
- Rankiteo TPRM Scoring methodology: https://static.rankiteo.com/model/rankiteo_tprm_methodology.pdf