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Mozilla Publishes Results of VPN Security Audit

Mozilla announced on Tuesday that it has made public a report detailing the results of a security audit targeting its Mozilla VPN product.

Officially launched in July 2020, Mozilla VPN is an open source virtual private network available as a browser extension, desktop application and mobile app. Mozilla VPN is currently available in 13 countries across North America, Europe and the APAC region.

Mozilla hired Germany-based security services provider Cure53 earlier this year to analyze the Mozilla VPN apps for Windows, Linux, macOS, iOS and Android, and this week it made the results of the audit public.

The analysis conducted by the company led to the discovery of one vulnerability and 15 “miscellaneous issues” that the researchers said did not lead to an exploit but could aid attackers in achieving their goals.

The vulnerability, classified as medium severity, could lead to user deanonymization if certain conditions are met — an attacker needs to be able to passively monitor network traffic, which typically only nation state threat actors can achieve. The flaw is related to a captive portal detection mechanism and Mozilla has determined that it would not patch it as the user benefits outweigh the security risk.

Of the miscellaneous issues, one has been classified as high severity and one as medium severity, with the remaining problems described as having low severity or being informational.

The high-severity issue is related to the VPN client exposing a WebSocket interface to the localhost when in debug mode. An attacker could have used this to obtain information from the targeted user by getting them to access a malicious website. However, customers were not affected as the impacted WebSocket interface was only used in pre-release test builds.

The medium-severity problem was related to the authentication flow used by VPN clients, and it could potentially result in an authorization code leak, but Mozilla said exploitation was prevented by the Content Security Policy (CSP) that is in place.

Mozilla addressed a majority of the problems in July, and Cure53 confirmed in August that the issues no longer exist.

This was the second audit by Cure53. The first, conducted in August 2020, led to the discovery of a bug that was classified as critical.

Cure53 has audited several major projects over the past years, including cURL, Dovecot, the Network Time Protocol (NTP), TunnelBear, and Firefox Accounts.

Related: SecureDrop Workstation Gets Post-Audit Security Refresh

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.