A flaw in GO SMS Pro App allows accessing media messages

An unpatched security flaw in GO SMS Pro, a popular messaging app for Android with over 100 million installs, exposes media messages.

GO SMS Pro is a popular Android messaging app with over 100 million installs, that has been found to be affected by an unpatched security flaw that publicly exposes media transferred between users.

An unauthenticated attacker could exploit the flaw to access any sensitive media shared between users of the app, including private voice messages, photos, and videos.

The flaw was discovered by researchers from Trustwave, it impacts version 7.91 of the app. The vulnerable version was uploaded to the Google Play Store on February 18, 2020.

“The GO SMS Pro application is a popular messenger app with over 100 million downloads and was discovered to publicly expose media transferred between users of the app.” reads the post published by Trustwave. “This exposure includes private voice messages, video messages, and photos.”

The experts noticed that if the recipient does not have the GO SMS Pro app installed, the app sends to the recipient an URL that points to media file via SMS. The recipient could then access the media file via a browser by clicking on the link.

SpiderLabs experts discovered that it is possible to access the link without any authentication or authorization, they also discovered that the URL link was sequential (hexadecimal) and predictable.

“Furthermore, when sharing media files, a link will be generated regardless of the recipient having the app installed.  As a result, a malicious user could potentially access any media files sent via this service and also any that are sent in the future. This obviously impacts the confidentiality of media content sent via this application.” continues the report.

An attacker can exploit the bug to generate a list of URLs and access user data without their knowledge.

The researchers also wrote a simple bash script to generate a sample list of URLs and demonstrate how an attacker could easily access masses of user data.

#!/bin/bash 
(echo obase=16; seq 1 $((echo ibase=16; echo FF) | bc)) | bc > 1
for i in $(cat 1); do echo "http://gs.3g.cn/D/dd1a$i /w"; done | tr -d " "

The cybersecurity firm attempted to contact the app developers multiple times since August 18, 2020, but received no reply.

Since then GO SMS Pro received two updates, but they still did not fix the flaw.

Below the timeline for the vulnerability:

• 08/18/2020 – Vendor contacted with no response
• 09/15/2020 – Vendor contacted with no response
• 10/14/2020 – Vendor contacted with no response
• 11/16/2020 – Vendor contacted with no response
• 11/19/2020 – Advisory published

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Pierluigi Paganini

(SecurityAffairs – hacking, GO SMS Pro)

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