Elasticsearch - Securing a search engine while maintaining usability

A presentation at JUG HH in August 2019 in Hamburg, Germany by Alexander Reelsen

Elasticsearch in 10 seconds Search Engine (FTS, Analytics, Geo), real-time Distributed, scalable, highly available, resilient Interface: HTTP & JSON Centrepiece of the Elastic Stack (Kibana, Logstash, Beats, APM, ML, Swiftype) Uneducated guess: Tens of thousands of clusters worldwide, hundreds of thousands of instances

Agenda Security: Feature or non-functional requirement? Security Manager Production Mode vs. Development Mode Plugins Scripting language: Painless

Security Feature or non-functional requirement?

Software has to be secure! O RLY? Defensive programming Do not persist specific data (PCI DSS) Not exploitable (pro tip: not gonna happen) No unintended resource access (directory traversal) Least privilege principle Reduced impact surface (DoS) https://www.theregister.co.uk/2017/03/26/miele_joins_internetofst_hall_of_shame/ Security as a non-functional requirement

Security as a feature Authentication Authorization (LDAP, users, PKI) TLS transport encryption Audit logging SSO/SAML/Kerberos

Security or resiliency? Integrity checks Preventing OOMEs Prevent deep pagination Do not expose credentials in cluster state/REST APISs Stop writing data before running out of disk space Unable to call System.exit

„[T]HERE ARE KNOWN KNOWNS; THERE ARE THINGS WE KNOW WE KNOW. WE ALSO KNOW THERE ARE KNOWN UNKNOWNS; THAT IS TO SAY WE KNOW THERE ARE SOME THINGS WE DO NOT KNOW. BUT THERE ARE ALSO UNKNOWN UNKNOWNS – THERE ARE THINGS WE DO NOT KNOW WE DON’T KNOW.“ Donald Rumsfeld, former secretary of defense, IT Security Expert

Security Manager Have you ever called System.setSecurityManager()?

Introduction Sandbox your java application Prevent certain calls by your application Policy file grants permissions FilePermission (read, write) SocketPermission (connect, listen, accept) URLPermission, PropertyPermission, …

OHAI JLS https://docs.oracle.com/javase/specs/jls/se11/html/jls-17.html#jls-17.5.3

Drawbacks Hardcoded policies before startup DNS lookups are cached forever by default Forces you to think about dependencies! Many libraries are not even tested with the security manager, unknown code paths may be executed No OOM protection! No stack overflow protection! Granularity No protection against java agents

Production mode vs Development mode Annoying you now instead of devastating you later

Is your dev setup equivalent to production? Development environments are rarely setup like production ones How to ensure certain preconditions in production but not for development? What is a good indicator?

Reducing impact Bad things have less bad results

Reducing impact Least privilege principle Do not run as root No chance of forking a process Do not expose sensitive settings Security Manager

Seccomp - prevent process forks Security manager could fail Elasticsearch should still not be able to fork processes One way transition to tell the operating system to deny execve, fork, vfork, execveat system calls Works on Linux, Windows, Solaris, BSD, osx

Security Manager in Elasticsearch Initialization required before starting security manager Elasticsearch needs to read its configuration file first to find out about the file paths Native code needs to be executed first Solution: Start with empty security manager, bootstrap, apply secure security manager

Security Manager in Elasticsearch Special security manager is used Does not set exitVM permissions, only a few special classes are allowed to call Thread & ThreadGroup security is enforced Also SpecialPermission was added, a special marker permission to prevent elevation by scripts

Security Manager in Elasticsearch ESPolicy allows for loading from files plus dynamic configuration (from the ES configuration file) Bootstrap check for java.security.AllPermission

Plugins in 60 seconds plugins are just zip files each plugin can have its own jars/dependencies each plugin is loaded with its own classloader each plugin can have its own security permissions ES core loads a bunch of code as modules (plugins that ship with Elasticsearch)

Introducing Painless A scripting language for Elasticsearch

Scripting: Why and how? Expression evaluation without needing to write java extensions for Elasticsearch Node ingest script processor Search queries (dynamic requests & fields) Aggregations (dynamic buckets) Templating (Mustache)

Scripting in Elasticsearch MVEL Groovy Expressions Painless

Painless - a secure scripting language Hard to take an existing programming language and make it secure, but remain fast Sandboxing Whitelisting over blacklisting, per method Opt-in to regular expressions Prevent endless loops Detect self references to prevent stack overflows

Summary Security is hard - let’s go shopping!

Summary Not using the Security Manager - what’s your excuse? Scripting is important, is your implementation secure? Use operating system features! If you allow for plugins, remain secure! If you remove features, have alternatives!

Thanks for listening! Questions? Alexander Reelsen @spinscale alex@elastic.co

Resources https://github.com/elastic/elasticsearch/ https://www.elastic.co/blog/bootstrap_checks_annoying_instead_of_devastating https://www.elastic.co/blog/scripting https://www.elastic.co/blog/scripting-security https://docs.oracle.com/javase/9/security/toc.htm https://docs.oracle.com/javase/9/security/permissions-java-development-kit.htm

Pagination: Request N C Find the first 10 results for Elasticsearch

Pagination: Request N N N C N N Find the first 10 results for Elasticsearch

Pagination: Query Phase N N SortedPriorityQueue size = 50 N C N N Each node returns 10 results, create real top 10 out of 50

Pagination: Fetch phase N N N C N N ask for the real top 10

Pagination: Query Phase N N N C N N return real top 10

Pagination: Query N N N C N N Find the 10 results starting at position 90

Pagination: Query Phase N N SortedPriorityQueue size = 500 N C N N Each node returns 100 results, create real top 90-100 out of 500

Pagination: Query N N N C N N Find the 10 results starting at position 99990

Pagination: Query Phase N N SortedPriorityQueue size = 500000 N C N N Each node returns 100k results

Pagination: Query 1 N N C N 100 Find the 10 results starting at position 99990 over 100 nodes

Pagination: Query 1 N SortedPriorityQueue size = 10_000_000 N C N 100 Each node returns 100k results

Solution: search_after Do not use numerical positions Use keys where you stopped in the inverted index Let the client tell you what the last key was Just specify the last sort value from the last document returned as a starting point

Pagination: search_after 1 N N C N 100 Find the 10 results starting at sort key name foo over 100 nodes

Pagination: search_after N N SortedPriorityQueue size = 1000 N C N N Each node returns 10 results

delete_by_query removal/replace delete_by_query API was not safe API endpoint was removed extensive documentation was added what to do instead infrastructure for long running background tasks was added delete_by_query was reintroduced using above infra and doing the exact same thing as in the documentation data > convenience!

Alexander Reelsen
@spinscale

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Elasticsearch - being an integral part of the Elastic Stack - is known for its full-text search and analytics ability.

Elasticsearch is running on tens of thousands of nodes world-wide, so despite all the functionality squeezed into new releases, we also have to think about security, all the time. This talk will cover different aspects of Elasticsearch, explain some features and (sometimes unpopular) decisions and the reasoning behind. This talk will cover:

Usage of the Java Security Manager including integration with plugins
Production vs. Development mode
System Call Filtering
Our own scripting language called Painless, which superseded all other scripting languages like MVEL, Groovy or Javascript

The goal of this talk is not (only) to show off Elasticsearch features. You start thinking about these non-functional requirements in your own applications as well!

Elasticsearch - Securing a search engine while maintaining usability

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