How to stop the “Gradle Snatchers”

Following on from one of the first recorded supply chain attacks against Gradle, this talk will discuss the security concerns surrounding our favorite build tool and how we can protect against them. This starts with gaining an understanding of some of Gradle's common vulnerabilities and how to avoid these within our Android projects. You'll leave this talk with:

- Insights on the Gradle Wrapper supply-chain attack and how to protect against it.
- An overview of a Gradle dependency attack and how to protect against them.
- A concrete list of security setting best practices within Gradle, including wrapper verification, repository filtering, dependency verification and others.

Transcript

1. @sp4ghetticode / spght.dev How to stop the 
 “Gradle Snatchers” Securing your builds from baddies Ed Holloway-George @ Droidcon Berlin 23
2. @sp4ghetticode / spght.dev Who am I? • Lead Android Dev @ ASOS • Android Google Dev Expert • I like to talk about mobile security a lot • Pomeranian Dad • Available on all good social media platforms (and also Twitter) • Danke fürs Kommen! I hope you learn something new Introduction
3. @sp4ghetticode / spght.dev Supply Chain Attacks A quick intro…
4. @sp4ghetticode / spght.dev Supply Chain Attacks Don’t let it happen to you!
5. @sp4ghetticode / spght.dev • Dependencies • Tooling • Helpers • Binaries What we will look at today
6. @sp4ghetticode / spght.dev Now let’s talk about the elephant in the room...
7. @sp4ghetticode / spght.dev
8. @sp4ghetticode / spght.dev Android & Gradle A timeline… 2008-2012 ‘The Eclipse Years’ Ant + ADT
9. @sp4ghetticode / spght.dev Android & Gradle A timeline… 2008-2012 ‘The Eclipse Years’ Ant + ADT The ‘Dark Ages'
10. @sp4ghetticode / spght.dev Android & Gradle 2008-2012 ‘The Eclipse Years’ Ant + ADT Fall 2012 ‘New Build Tool’ AGP v0.1 A timeline…
11. @sp4ghetticode / spght.dev Android & Gradle 2008-2012 ‘The Eclipse Years’ Ant + ADT Fall 2012 ‘New Build Tool’ AGP v0.1 Winter 2014 ‘Initial Release’ AGP v1.0 A timeline…
12. @sp4ghetticode / spght.dev l 2012 uild Tool’ P v0.1 Winter 2014 ‘Initial Release’ AGP v1.0 2023 
 Present Day AGP v8.x Android & Gradle A timeline…
13. @sp4ghetticode / spght.dev l 2012 uild Tool’ P v0.1 Winter 2014 ‘Initial Release’ AGP v1.0 2023 
 Present Day AGP v8.x Android & Gradle A timeline… Winter 2018 
 ‘A Confusing Dependency’
14. @sp4ghetticode / spght.dev Márton Braun @zsmb13 A Confusing Dependency…
15. @sp4ghetticode / spght.dev Márton Braun @zsmb13 A Confusing Dependency… com.example:foo:0.0.1 jitpack.io FROM
16. @sp4ghetticode / spght.dev Márton Braun @zsmb13 A Confusing Dependency… java.lang.SecurityException: Permission denied (missing INTERNET permission?) at java.net.Inet6AddressImpl.lookupHostByName(Inet6AddressImpl.java:135) at java.net.Inet6AddressImpl.lookupAllHostAddr(Inet6AddressImpl.java:90) at java.net.InetAddress.getByName(InetAddress.java:743) 💧
17. @sp4ghetticode / spght.dev ???
18. @sp4ghetticode / spght.dev Márton Braun @zsmb13 A Confusing Dependency… repositories { google() jcenter() maven { url "https://jitpack.io" } } dependencies { implementation ‘com.example:foo:0.0.1’ }
19. @sp4ghetticode / spght.dev A Confusing Dependency… repositories { google() jcenter() maven { url "https://jitpack.io" } } dependencies { implementation 'com.example:foo:0.0.1' }
20. @sp4ghetticode / spght.dev A Confusing Dependency… com.example:foo:0.0.1 repositories { google() jcenter() maven { url "https://jitpack.io" } } dependencies { implementation 'com.example:foo:0.0.1' } Does not exist
21. @sp4ghetticode / spght.dev A Confusing Dependency… com.example:foo:0.0.1 repositories { google() jcenter() maven { url "https://jitpack.io" } } dependencies { implementation 'com.example:foo:0.0.1' } Shouldn’t exist…
22. @sp4ghetticode / spght.dev Introducing: ‘Fake Wharton’
23. @sp4ghetticode / spght.dev A Confusing Dependency… jakewhaarton/timber/com.example:foo:0.0.1 repositories { google() jcenter() maven { url "https://jitpack.io" } } dependencies { implementation 'com.example:foo:0.0.1' }
24. @sp4ghetticode / spght.dev A Confusing Dependency… jakewhaarton/timber/com.example:foo:0.0.1 repositories { google() jcenter() maven { url "https://jitpack.io" } } dependencies { implementation ‘com.example:foo:0.0.1' }
25. @sp4ghetticode / spght.dev A Confusing Dependency… jakewhaarton/timber/com.example:foo:0.0.1 repositories { google() jcenter() maven { url "https://jitpack.io" } } dependencies { implementation 'com.example:foo:0.0.1' }
26. @sp4ghetticode / spght.dev Long story short…
27. @sp4ghetticode / spght.dev
28. @sp4ghetticode / spght.dev Trust no one Original write-up link available @ spght.dev/talks (Thanks Márton!)
29. @sp4ghetticode / spght.dev Dependency Verification
30. @sp4ghetticode / spght.dev Dependency Verification • Are my app’s dependencies legitimate? • Is integrity compromised? • Is the origin compromised? • What about transitive dependencies?
31. @sp4ghetticode / spght.dev • Gradle offers a solution for both • Checksum Verification • Signature Verification Dependency Verification
32. @sp4ghetticode / spght.dev Checksum Verification
33. @sp4ghetticode / spght.dev Checksum Verification Example • Common algorithms to use MD5 / SHA-1 / SHA-256 • MD5 was proved to be broken in late 90s • SHA-1 also proved to be broken in 2017
34. @sp4ghetticode / spght.dev Checksum Verification Example $ echo "Hello World" >> example.txt 
 SHA-1 $ shasum example.txt 648a6a6ffffdaa0badb23… 
 SHA-256 $ shasum -a 256 example.txt d2a84f4b8b650937ec8f73…
35. @sp4ghetticode / spght.dev Gradle Dependency Setup ./gradlew --write-verification-metadata sha256 <task>
36. @sp4ghetticode / spght.dev Gradle Dependency Setup ./gradlew --write-verification-metadata sha256 {project root}/gradle/verification-metadata.xml
37. @sp4ghetticode / spght.dev Gradle Dependency Setup ./gradlew --write-verification-metadata sha256 <verification-metadata> <configuration> <verify-metadata>true</verify-metadata> <verify-signatures>false</verify-signatures> </configuration> <components>…</components> </verification-metadata> {project root}/gradle/verification-metadata.xml
38. @sp4ghetticode / spght.dev Gradle Dependency Setup ./gradlew --write-verification-metadata sha256 <components> 
 <component group="com.jakewharton.timber" name="timber" version="5.0.1"> <artifact name="timber-5.0.1.aar"> <sha256 value="c6edddfc..." origin="Generated by Gradle"/> <sha512 value="37a3e784..." origin="Generated by Gradle"/> </artifact> </component> </components> {project root}/gradle/verification-metadata.xml
39. @sp4ghetticode / spght.dev How it works… Maven Repo
40. @sp4ghetticode / spght.dev How it works… <components> 
 <component group="com.jakewharton.timber" name="timber" version="5.0.1"> <artifact name="timber-5.0.1.aar"> <sha256 value="c6edddfc..." origin="Generated by Gradle"/> <sha512 value="37a3e784..." origin="Generated by Gradle"/> </artifact> </component> </components> .sha256 .sha512 Maven Repo
41. @sp4ghetticode / spght.dev Reporting issues <components> 
 <component group="com.jakewharton.timber" name="timber" version="5.0.1"> <artifact name="timber-5.0.1.aar"> <sha256 value="ffedddfc..." origin="Generated by Gradle"/> <sha512 value="ffa3e784..." origin="Generated by Gradle"/> </artifact> </component> </components>
42. @sp4ghetticode / spght.dev Reporting issues <components> 
 <component group="com.jakewharton.timber" name="timber" version="5.0.1"> <artifact name="timber-5.0.1.aar"> <sha256 value="ffedddfc..." origin="Generated by Gradle"/> <sha512 value="ffa3e784..." origin="Generated by Gradle"/> </artifact> </component> </components>
43. @sp4ghetticode / spght.dev Reporting issues <components> 
 <component group="com.jakewharton.timber" name="timber" version="5.0.1"> <artifact name="timber-5.0.1.aar"> <sha256 value="ffedddfc..." origin="Generated by Gradle"/> <sha512 value="ffa3e784..." origin="Generated by Gradle"/> </artifact> </component> </components> {project root}/gradle.properties org.gradle.dependency.verification.console=verbose
44. @sp4ghetticode / spght.dev Reporting issues <components> 
 <component group="com.jakewharton.timber" name="timber" version="5.0.1"> <artifact name="timber-5.0.1.aar"> <sha256 value="ffedddfc..." origin="Generated by Gradle"/> <sha512 value="ffa3e784..." origin="Generated by Gradle"/> </artifact> </component> </components> {project root}/build/reports/dependency-verification
45. @sp4ghetticode / spght.dev Signature Verification
46. @sp4ghetticode / spght.dev Signature Verification Example • Public Maven repos often require signed artifacts • Signed using PGP standard • Developer must create a key-pair • Upload public key to key-server • Sign artifacts and upload to Maven repo
47. @sp4ghetticode / spght.dev Gradle Dependency Setup ./gradlew --write-verification-metadata sha256,pgp
48. @sp4ghetticode / spght.dev Gradle Dependency Setup ./gradlew --write-verification-metadata sha256,pgp <verification-metadata> <configuration> <verify-metadata>true</verify-metadata> <verify-signatures>true</verify-signatures> </configuration> <trusted-keys>…</trusted-keys> </verification-metadata> {project root}/gradle/verification-metadata.xml
49. @sp4ghetticode / spght.dev Gradle Dependency Setup ./gradlew --write-verification-metadata sha256,pgp <trusted-keys> 
 <trusted-key id=“47bf5922…” group="com.jakewharton.timber" name=“timber" version="5.0.1"/> </trusted-keys> {project root}/gradle/verification-metadata.xml
50. @sp4ghetticode / spght.dev How it works… Maven Repo
51. @sp4ghetticode / spght.dev How it works… .asc Maven Repo timber-5.0.1.aar timber-5.0.1.aar.asc
52. @sp4ghetticode / spght.dev How it works…
53. @sp4ghetticode / spght.dev Dependency Verification The pros… • Gain trust in your app’s dependencies • Flexible in the type of verification you wish to use Supply chain attacks mitigated • You will sleep a lot easier at night! (and so will I)
54. @sp4ghetticode / spght.dev The cons… • This is not a frictionless process • You MUST start with total trust in the dependencies • You could still include compromised dependencies • XML 💩 • Simplest solution: Ship with no dependencies! (Yes, really 😅) Dependency Verification
55. @sp4ghetticode / spght.dev Repository Filter • Filter what packages can be fetched from repos • Rules to include and exclude dependencies • Works for dependencies and plugins • Note: Use Gradle 7.0+ (Due to CVE-2021-29427)* * Discovered by Droidcon regular @ZacSweers
56. @sp4ghetticode / spght.dev Repository Filter repositories { maven { url "https://jitpack.io" content { // Fetch dependencies includeGroup "com.example" includeModule("com.example", “foo”) // Exclude dependencies 
 excludeGroupByRegex("dev\\.spght\\..*") } } }
57. @sp4ghetticode / spght.dev Repository Filter • Gain trust your dependencies come from the right source • Ordering issues eliminated • Can easily create simple or complex rulesets • Do not leak dependencies by calling multiple repos * Discovered by Droidcon regular @ZacSweers
58. @sp4ghetticode / spght.dev l 2012 uild Tool’ P v0.1 Winter 2014 ‘Initial Release’ AGP v1.0 2023 
 Present Day AGP v8.x Android & Gradle A timeline… Winter 2018 
 ‘A Confusing Dependency’
59. @sp4ghetticode / spght.dev 014 lease’ 0 2023 
 Present Day AGP v8.x Android & Gradle A timeline… Winter 2018 
 ‘A Confusing Dependency’ Winter 2022 
 ‘Wrapper Exploit Observed’
60. @sp4ghetticode / spght.dev Where’s a great place to see hacking in the wild?
62. @sp4ghetticode / spght.dev (It’s relevant I promise) • MinecraftOnline.com • Oldest multiplayer Minecraft Server (2010- present) • 290,000 unique players Background
63. @sp4ghetticode / spght.dev (It’s relevant I promise) • Minecraft servers use ‘plugins’ • Plugins are JVM language projects (like Android) • Gradle is the build system used (like Android) Background
64. @sp4ghetticode / spght.dev Banned Player What happened?
65. @sp4ghetticode / spght.dev What happened? Totally Legit Player
66. @sp4ghetticode / spght.dev What happened? Totally Legit Dev-Team Member
67. @sp4ghetticode / spght.dev What happened? Totally Legit Dev-Team Member Malicious Commit 😈
68. @sp4ghetticode / spght.dev What happened? Totally Legit Dev-Team Member
69. @sp4ghetticode / spght.dev How to prevent this! • First known public supply-chain attack on the Wrapper • Verification of wrapper’s integrity prevents this • Verification of Gradle binary is a good second step • Hashes of wrapper and distributions available • gradle.org/release-checksums
70. @sp4ghetticode / spght.dev Gradle Wrapper Verification Verification Script gist.github.com/ed-george/3751d09ccdfd33cfe48d8987d9f68510
71. @sp4ghetticode / spght.dev Gradle Wrapper Verification Github Action github.com/marketplace/actions/gradle-wrapper-validation
72. @sp4ghetticode / spght.dev Verifying the Wrapper The pros… • Mega straightforward • You could probably do it before I finish this talk • Easily slips into most CI pipelines • GitHub users pretty much get it for free
73. @sp4ghetticode / spght.dev Verifying the Wrapper The cons… • Still fairly unlikely to be an attack vector • Otherwise, no other cons (that I can think of)!
74. @sp4ghetticode / spght.dev Verifying the Distribution {project root}/gradle/wrapper/gradle-wrapper.properties 
 
 distributionUrl=https\://services.gradle.org/distributions/gradle-7.5-bin.zip
75. @sp4ghetticode / spght.dev Verifying the Distribution {project root}/gradle/wrapper/gradle-wrapper.properties distributionUrl=https\://services.gradle.org/distributions/gradle-7.5-bin.zip distributionSha256Sum=cb87f222c5585bd46838ad4…
76. @sp4ghetticode / spght.dev Verifying the Distribution ./gradlew wrapper --gradle-version=7.5 \ --gradle-distribution-sha256-sum=cb87f222c…
77. @sp4ghetticode / spght.dev Verifying the Distribution
78. @sp4ghetticode / spght.dev Verifying the Distribution The pros… • Guarantees integrity of your Gradle distro • Simple to setup • Verification is quick
79. @sp4ghetticode / spght.dev Verifying the Distribution The cons… • Remembering to update via wrapper command and flag • Again, not many other cons (that I can think of)!
80. @sp4ghetticode / spght.dev Verifying the gradlew file (Not yet) • The gradlew script is also often overlooked • No official process for verifying • Roll your own solution • Have thorough PR review processes!
81. @sp4ghetticode / spght.dev Verifying the gradlew file (Not yet)
82. @sp4ghetticode / spght.dev Summary
83. @sp4ghetticode / spght.dev In summary… • Gradle supply-chain attacks are very rare but do occur • Consider dependency verification • Use repository filtering to ensure the origin • Verify your wrappers • Verify your distribution
84. @sp4ghetticode / spght.dev I want to learn more… (Perhaps from someone better?!) • Great talk by Cédric Champeau from Gradle at Devoxx 2019 • Gradle Security documentation • Speak to a nice human at Gradle booth @ Droidcon
85. @sp4ghetticode / spght.dev spght.dev/talks For more in-depth Mobile Security talks/blogs
86. @sp4ghetticode / spght.dev spght.dev/talks Would really appreciate 👍 via the talk feedback in-app
87. @sp4ghetticode / spght.dev Thanks! spght.dev/talks
88. @sp4ghetticode / spght.dev EOF spght.dev/talks