The Pidgin messaging app removed the ScreenShareOTR plugin from its official third-party plugin list after it was discovered that it was used to install keyloggers, information stealers, and malware commonly used to gain initial access to corporate networks.

The plugin was promoted as a screen-sharing tool for secure Off-The-Record (OTR) protocol and was available for both Windows and Linux versions of Pidgin.

According to ESET, the malicious plugin was configured to infect unsuspecting users with DarkGate malware, a powerful malware threat actors use to breach networks since QBot’s dismantling by the authorities.

Sneaky Pidgin plugin

Pidgin is an open-source, cross-platform instant messaging client that supports multiple networks and messaging protocols.

Although not as popular as in the mid-2000s when multi-protocol clients were in high demand, it remains a popular choice among those seeking to consolidate their messaging accounts into a single app and has a dedicated user base of tech-savvy individuals, open-source enthusiasts, and users who need to connect to legacy IM systems.

Pidgin operates a plugin system that allows users to extend the program’s functionality, enable niche features, and unlock new customization options.

Users can download them from the project’s official third-party plugins list, currently hosting 211 addons.

According to an announcement on the project’s website last week, a malicious plugin named ‘ss-otr’ had slipped into the list on July 6, 2024, and was only pulled on August 16 following a user report about it being a keylogger and screenshot capturing tool.

A red flag is that ss-otr only provided binaries for download and not any source code, but due to the lack of robust reviewing mechanisms in Pidgin’s third-party plugin repository, nobody questioned its security.

Plugin leads to DarkGate malware

ESET reports the plugin installer is signed with a valid digital certificate issued to INTERREX – SP. Z O.O., a legitimate Polish company.

The plugin offers the advertised functionality of screen sharing but also contains malicious code, allowing it to download additional binaries from the attacker’s server at jabberplugins[.]net.

The downloaded payloads are either PowerShell scripts or the DarkGate malware, which is also signed by an Interrex certificate.

A similar mechanism is implemented for the Linux version of the Pidgin client, so both platforms are covered.

ESET says that the same malicious server, which has been taken down now, hosted additional plugins named OMEMO, Pidgin Paranoia, Master Password, Window Merge, and HTTP File Upload.

These plugins were almost certainly also delivering DarkGate, indicating that ScreenShareOTR was just one small part of a broader-scale campaign.

Pidgin has not provided download stats for ss-otr, so the number of victims is unknown. 

Those who installed it are recommended to remove it immediately and perform a full system scan with an antivirus tool, as DarkGate may be lurking on their system.

To prevent similar incidents from happening in the future, Pidgin announced that, from now on, it will only accept third-party plugins that have an OSI Approved Open Source License, allowing scrutiny into their code and internal functionality.