Pierluigi Paganini
April 05, 2025
A now-patched vulnerability in Verizon ’s iOS Call Filter app could have been exploited to harvest the call records of millions of Americans.
Verizon’s Call Filter app allows users to identify and manage unwanted calls, such as spam and robocalls. It offers features like spam detection, automatic blocking of high-risk spam calls, and the ability to report unwanted numbers. The app is available for iOS devices and can be downloaded from the App Store.
The researchers Evan Connelly reported the flaw to Verizon on February 22, 2025, the vulnerability was addressed in mid-March.
“Imagine if anyone could punch in a phone number from the largest U.S. cell carrier and instantly retrieve a list of its recent incoming calls—complete with timestamps—without compromising the device, guessing a password, or alerting the user.” warned the expert. “Now imagine that number belongs to a journalist, a police officer, a politician, or someone fleeing an abuser.”
Connelly analyzed the traffic from the app and the server and found that Verizon’s app requested call data from a server using a phone number and time range. The process lacks ownership verification, potentially allowing malicious actors to obtain incoming call records for any number by crafting a request using the target’s phone number.
The vulnerability in the Verizon Call Filter app’s /clr/callLogRetrieval endpoint, although authentication was enforced via JWT tokens, the server failed to verify that the phone number in the header matched the token’s user ID (sub). As a result, attackers could retrieve call histories for arbitrary numbers. The issue likely affected most Verizon Wireless users, as the service is often enabled by default.
Connelly explained that an attacker can retrieve timestamps associated with incoming calls, exploiting this vulnerability. Call metadata can enable real-time surveillance if misused. With access to call history, attackers can map routines, contacts, and movements, risking the safety of whistleblowers, journalists, dissidents, and others. Repeated numbers may reveal private or burner lines. Though it may seem minor, this wasn’t just a data leak, it was a powerful tool that could be exploited for tracking and profiling individuals.
The researcher discovered that the API for Verizon’s Call Filter app is hosted on a domain (“CEQUINTVZWECID.com”) registered via GoDaddy, which is unusual for a major company. The domain name suggests it’s linked to Cequint, a telecom tech firm specializing in caller ID, which likely operates the backend. Since Cequint’s own website is down, concerns arise about how much user data this lesser-known company holds—and how securely it’s managed.
Below is the timeline for this vulnerability:
Connelly credited Verizon for a quick response and fix. The carrier states that the flaw wasn’t exploited and affected only iOS devices.
“While there was no indication that the flaw was exploited, the issue was resolved and only impacted iOS devices. Verizon appreciates the responsible disclosure of the finding by the researcher and takes the security very seriously,” Verizon said in a statement.
Recently, media reported that a China-linked cyber espionage group is targeting several telecom companies demonstrating that call data may be valuable to threat actors.
(SecurityAffairs – hacking, Verizon)
