Security Advisory 2021-08-01-3 - luci-app-ddns: Multiple authenticated RCEs (CVE-2021-28961)

DESCRIPTION
An authenticated user in LuCI is able to inject shell code in luci-app-ddns. Multiple variables in the luci-app-ddns applications where not validated before they were executed on the system’s shell, which could be exploited by adding system shell commands.

REQUIREMENTS
To exploit this vulnerability the attackers needs access to LuCI and the extra application luci-app-ddns has to be installed. The attacker is then able to inject code which is executed on the shell of the system.

In a normal OpenWrt installation all users that have access to LuCI also have access to the shell of the system over SSH for example by design.
*[SSH]: Secure Shell

AFFECTED VERSIONS
To our knowledge, OpenWrt version 19.07.0 to 19.07.7 are affected. The fixed packages will be integrated in the upcoming OpenWrt 19.07.8 release. Older versions of OpenWrt (e.g. OpenWrt 18.06, OpenWrt 15.05 and LEDE 17.01) are end of life and not supported any more.

In OpenWrt 21.02 the luci-app-ddns package was already convert to a client side implementation which is not affected by this problem.

CREDITS
This issue was identified by Jussi Rämo (Ericsson Product Security Assurance Team).