The remote Debian host is missing a security-related update.
Several vulnerabilities were discovered in jruby, a Java implementation of the Ruby programming language. They would allow an attacker to use specially crafted gem files to mount cross-site scripting attacks, cause denial of service through an infinite loop, write arbitrary files, or run malicious code.
Upgrade the jruby packages. For the stable distribution (stretch), these problems have been fixed in version 1.7.26-1+deb9u1. In addition, this message serves as an announcement that security support for jruby in the Debian 8 oldstable release (jessie) is now discontinued. Users of jruby in Debian 8 that want security updates are strongly encouraged to upgrade now to the current Debian 9 stable release (stretch).