Eurofiber France Customer Data Breach: Hacker Attempts to Sell Compromised Information from Customer Data Systems

Executive Summary

Eurofiber France has issued a warning regarding a data breach after a threat actor attempted to sell customer data online. The incident was detected when a hacker advertised what was claimed to be customer information from Eurofiber France on a cybercrime forum. The company has confirmed that unauthorized access to its systems occurred, potentially exposing sensitive customer data. At this stage, the full scope of the breach, including the specific data types compromised and the number of affected customers, is still under investigation. Eurofiber France has notified relevant authorities and is working with cybersecurity experts to assess the impact and contain the incident. Customers are advised to remain vigilant for suspicious communications and to follow any guidance provided by Eurofiber France.

Technical Information

The breach at Eurofiber France was identified following the appearance of a data set for sale on a well-known cybercrime forum. The threat actor claimed to possess customer data, which prompted an immediate internal investigation by Eurofiber France. The company confirmed that an unauthorized party had accessed its systems, although the precise attack vector has not yet been publicly disclosed.

Initial analysis suggests that the attacker may have exploited a vulnerability in the company’s external-facing infrastructure or leveraged compromised credentials to gain access. The lack of detailed technical indicators of compromise (IOCs) at this stage limits the ability to attribute the breach to a specific malware family, toolset, or threat group. However, the modus operandi—unauthorized access followed by data exfiltration and subsequent sale—aligns with tactics observed in recent financially motivated cyberattacks targeting telecommunications and infrastructure providers.

The compromised data reportedly includes customer contact information, service details, and potentially other personally identifiable information (PII). The quality of evidence regarding the data set’s authenticity is currently based on the threat actor’s claims and partial data samples shared on the forum. Eurofiber France is conducting forensic analysis to validate the scope and authenticity of the leaked data.

The incident highlights the ongoing risks associated with third-party access, credential management, and perimeter security for organizations operating critical infrastructure. The breach underscores the importance of robust monitoring, rapid incident response, and transparent communication with affected stakeholders.

Affected Versions & Timeline

The breach specifically impacts Eurofiber France’s customer data systems. At this time, there is no public evidence indicating that other Eurofiber entities or systems outside of France are affected. The timeline of the incident is as follows: the initial unauthorized access is believed to have occurred in the days leading up to the public data sale offer, which was detected and reported in early June 2025. Eurofiber France became aware of the incident after the hacker’s post was identified on a cybercrime forum and immediately initiated an internal investigation.

The company has not yet disclosed the specific software versions, platforms, or infrastructure components involved in the breach. The investigation is ongoing, and further details regarding affected systems and the duration of unauthorized access are expected to be released as the forensic analysis progresses.

Threat Activity

The threat actor involved in the Eurofiber France breach demonstrated typical behavior associated with financially motivated cybercriminals. After gaining unauthorized access to the company’s systems, the attacker exfiltrated customer data and attempted to monetize the breach by offering the data for sale on a cybercrime forum. The forum post included sample records to validate the authenticity of the data and attract potential buyers.

There is currently no evidence to suggest that ransomware or destructive malware was deployed as part of this incident. The primary objective appears to have been data theft for financial gain. The tactics, techniques, and procedures (TTPs) observed are consistent with those documented in the MITRE ATT&CK framework under Initial Access (T1078: Valid Accounts), Exfiltration (T1041: Exfiltration Over C2 Channel), and Impact (T1496: Data Encrypted for Impact), although the latter is not confirmed in this case.

The threat actor’s identity and affiliation remain unknown. The use of a cybercrime forum for data sale is a common practice among both individual hackers and organized cybercriminal groups. The incident has not, at this time, been linked to any known advanced persistent threat (APT) group.

Mitigation & Workarounds

Eurofiber France has taken immediate steps to contain the breach and mitigate further risk. The company has notified relevant data protection authorities and is cooperating with law enforcement. Customers have been advised to monitor their accounts for suspicious activity, be cautious of phishing attempts, and follow any additional security guidance provided by Eurofiber France.

Critical mitigation actions include resetting potentially compromised credentials, enhancing monitoring of network and system activity, and conducting a comprehensive review of access controls. High-priority recommendations for customers include enabling multi-factor authentication (MFA) where available, updating passwords, and remaining alert to unsolicited communications that may attempt to exploit the breach.

Medium-priority actions involve reviewing account activity for unauthorized changes and ensuring that contact information is up to date with Eurofiber France. Low-priority recommendations include staying informed about the ongoing investigation and following updates from the company and relevant authorities.

At this stage, no specific software patches or technical workarounds have been announced, as the root cause of the breach is still under investigation. Customers should continue to follow best practices for account security and data protection.

References

As of this writing, direct URLs to primary sources are unavailable due to technical limitations. Customers are encouraged to monitor official communications from Eurofiber France and reputable cybersecurity news outlets for updates on the incident.

About Rescana

Rescana provides a Third-Party Risk Management (TPRM) platform designed to help organizations identify, assess, and monitor risks associated with their external partners and vendors. Our platform enables continuous visibility into third-party security posture, supports rapid incident response, and facilitates compliance with regulatory requirements. For questions or further information, please contact us at ops@rescana.com.