Yahoo, Equifax Serve as Cautionary Tales in Discerning Data Breach Scope

Yahoo and Equifax's separate disclosures this week that previously reported data breaches at their organizations were even bigger than first thought illuminated the massive challenge enterprises face in gauging the true scope of malicious intrusions these days.

Yahoo's parent company Verizon on Tuesday said an August 2013 breach that Yahoo disclosed in Dec. 2016 impacted a mind-boggling three billion email accounts rather than the one billion figure originally reported. 

Following Verizon's acquisition of Yahoo and during the integration of the two companies, Yahoo obtained new information showing that every single one of its user accounts in August 2013 was compromised, Verizon subsidiary Oath said in a statement. The investigation showed that the data that was stolen did not include, however, clear text passwords, payment card data, or bank account information, the company said.

In a similar update the day before, Equifax said that the actual number of people impacted by the breach it disclosed on Sept. 7 was 145.5 million, or 2.5 million more than the number it had first reported. The company said a forensic analysis conducted by cybersecurity firm Mandiant unearthed the additional victims. The investigation showed that no databases outside the US were impacted, Equifax said, while also revising downward the number of Canadian victims impacted from 100,000 to 8,000.

Nathan Wenzler, chief security strategist at security consulting firm AsTech, says multiple factors can make it hard for organizations to get a true handle on the scope of intrusions such as the ones at Yahoo and Equifax. "Most of it centers on the lack of sound asset management and inventory processes," he says.

Many organizations don't actually know what they have to begin with, and therefore struggle to figure out what was breached when an incident occurs. "And, to be fair, a lot of hackers don't make it easy to figure out either," Wenzler says. "Systems can be compromised quietly, with no trace of anything serious being done, which can make it difficult for a researcher to know for certain that a system was compromised."

Companies with a less than perfect understanding of their assets are likely to keep discovering more datasets that have been compromised than they originally assumed when investigating a breach incident, he says.

CEO in the Hotseat

Equifax's update this week added to broad concerns over its response to the breach overall, including its 45-day delay in breach notification and its inavertently pointing those wanting to sign up for free credit monitoring to a phishing website.

Former Equifax CEO Richard Smith, who retired from the company after the breach, this week acknowledged mistakes with the rollout of the signup website and call centers. In many cases, such issues added to the frustration of American consumers, he said in prepared testimony for a US House Committee on Energy and Commerce subcommittee, which held a hearing on the breach this week.

The testimony delved into some details of the incident. Smith noted that when Equifax's security organization first heard from US-CERT about an Apache Struts vulnerability that needed to be patched, the information was promptly relayed to all applicable personnel. However, the vulnerability remained unpatched and was not caught in subsequent scans, giving the intruders a way into Equifax's network.

In some cases, organizations that suffer large, sophisticated breaches will never know the full scope of its impact, says Michael Sutton, CISO at Zscaler. With Yahoo, there's no information on what new evidence led it to the two billion additional breached accounts one year after the original discovery. That the initial investigation failed to catch such a huge number of compromised accounts is significant, he says.

"While it’s possible that new evidence, such as logs were uncovered that hadn’t previously been reviewed, more likely a new connection was made," he says. "Breach investigations are all about connecting the dots — identifying an entry point and figuring out where the attacker went from there," he says. "Without transparency from Yahoo, we can only speculate as to what new dots were connected."

Generally, determining the full scope of an incident can be hard when multiple entry points are involved and when multiple devices or accounts are compromised, Sutton notes.

Investigators had a hard time figuring out what was stolen from Equifax because the records were stored in various data tables across multiple systems, according to the CEO's testimony. So tracing the records back to specific individuals, given the massive scope of the compromise, was very time consuming and difficult, he said.

The telltale signs of such attacks can be scattered and hard to find even if they exist. "Following the trail of breadcrumbs to trace the attacker's path requires that the bread crumbs exist in the first place," Sutton says. "It’s possible that logs have blind spots or have been overwritten, especially when a breach investigation takes places months or years after the incident."

Backup logs are one place where a breached entity might discover more records than were originally presumed compromised in an incident, says Alex Held, chief research officer at SecurityScorecard.

Attackers can put in a lot of effort to erase evidence of unauthorized access following a successful attack. Log removal is often the final step in this effort because it can blur the true scope of the incident and make attribution difficult. In such situations, a backup logs that may not have been available during the initial investigation can shed fresh light on the true scope of the incident, he says.

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