[Original blog post here: https://wwws.nightwatchcybersecurity.com/2019/02/07/content-injection-in-amazon-kindles-fireos-cve-2019-7399/] SUMMARY The FireOS operating system provided by Amazon for Fire tablet devices can be injected with malicious content by an MITM attacker. An attacker can also capture the serial number of the device. The root cause is lack of HTTPS for legal content (terms of use and privacy policy) within the settings section. The issue was discovered in FireOS v5.3.6.3 and fixed by the vendor in v5.3.6.4 that was released in November 2018. Devices will automatically update to the latest version. CVE-2019-7399 has been assigned by MITRE to track this issue. VULNERABILITY DETAILS FireOS is an operating system provided by Amazon for the Fire tablet devices. It is a customized fork of Android. While monitoring network traffic on a test device, we observed that several calls from the settings section (terms of use and privacy policy) are done without HTTPS and can be injected with malicious content by an MITM attacker. It is also possible for the attacker to observe this traffic and capture the serial number (DSN) of the device. Steps To Replicate (on Ubuntu 18.04) 1. Install the application on the Android device but do not start it. 2. Install dnsmasq and NGINX on the Linux host: sudo apt-get install dnsmasq nginx 3. Modify the /etc/hosts file to add the following entry to map the domain name to the Linux host: 192.168.1.x www.kindle.com 192.168.1.x kindle.com 4. Configure /etc/dnsmasq.conf file to listen on the IP and restart DNSMASQ listen-address=192.168.1.x sudo /etc/init.d/dnsmasq restart 5. Add a file with malicious content (you may need to use sudo): cd /var/www/html mkdir support echo powned >support/privacy echo powned >support/terms 6. Modify the settings on the Kindle device to static, set DNS to point to a192.168.1.xa. AT THIS POINT a the Kindle device will resolve DNS against the Linux computer and serve the large servers file 7. Tap aSettingsa, aLegal and Compliancea, and tap either aTerms of Usea or aPrivacya. Observe injected content. VENDOR RESPONSE AND MITIGATION The issue was discovered in FireOS v5.3.6.3 and fixed by the vendor in v5.3.6.4 that was released in November 2018. Devices will automatically update to the latest version. MITRE assigned CVE-2019-7399 to track this issue. REFERENCES Amazon tracking # PO135449968 CVE-ID: CVE-2019-7399 CREDITS Text of the advisory written by Yakov Shafranovich. TIMELINE 2018-09-03: Initial report to the vendor 2018-09-04: Report triaged and being reviewed by the vendor 2018-09-17: Communication from the vendor, issue still being reviewed 2019-01-10: Fix confirmed, communication regarding disclosure 2019-01-30: Vendor pinged about CVE assignment 2019-02-03: Draft advisory sent for review 2019-02-04: CVE issued by MITRE 2019-02-07: Public disclosure; minor syntax updates