Firebase APK Security Scanner

What it does

When your agent uses it

• Auditing an Android app for Firebase security misconfigurations
• Checking whether Firebase endpoints found in an APK allow unauthenticated access
• Enumerating Cloud Functions during an authorized penetration test
• Running a mobile security assessment of a Firebase-backed app

Example prompts

• “Scan ./builds/app-release.apk for Firebase misconfigurations. We own this app and have approval to test it.”
• “Check the staging build in ./apks/staging for open storage buckets and anonymous auth.”
• “Do the Cloud Functions referenced in our own Android app accept unauthenticated calls?”

Requirements

• apktool and curl
• An APK file or directory to scan
• Explicit authorization to test the target app
• Pre-approved tools (allowed-tools): Bash({baseDir}/scanner.sh:*), Bash(apktool:*), Bash(curl:*), Read, Grep, Glob

Workflow steps

3 steps, taken from the step headings in SKILL.md.

1. 1Validate Input
2. 2Run the Scanner
3. 3Present Results

What it can do on your machine

Read from SKILL.md and the folder at commit 82fe822. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves these tools, so the agent can use them without asking each time:

  • Bash({baseDir}/scanner.sh:*)
  • Bash(apktool:*)
  • Bash(curl:*)
  • Read
  • Grep
  • Glob

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Ships script files (Shell), which the agent can run.

  Shell commands in SKILL.md call:

  • curl

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Hosts in commands or code, which the agent is likely to contact:

  • identitytoolkit.googleapis.com
  • firestore.googleapis.com
  • firebasestorage.googleapis.com
  • firebaseremoteconfig.googleapis.com

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names these keys or tokens, usually read from environment variables:

  • API_KEY

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Firebase APK Security Scanner loads about 1.8k tokens when it runs, and up to ~7.1k if it reads all its reference files. Until then it costs about 88 tokens; SKILL.md has 709 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~88

When it runs · the whole SKILL.md, loaded when a task matches

~1.8k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~7.1k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from trailofbits/skills at commit 82fe822, republished under its CC-BY-SA-4.0 licence (© trailofbits). 709 words, ~1,842 tokens.

name

firebase-apk-scanner

description

Scans Android APKs for Firebase security misconfigurations including open databases, storage buckets, authentication issues, and exposed cloud functions. Use when analyzing APK files for Firebase vulnerabilities, performing mobile app security audits, or testing Firebase endpoint security. For authorized security research only.

allowed-tools

Bash({baseDir}/scanner.sh:*), Bash(apktool:*), Bash(curl:*), Read, Grep, Glob

argument-hint

apk-file-or-directory

disable-model-invocation

true

ls -la $ARGUMENTS

{baseDir}/scanner.sh $ARGUMENTS

cat firebase_scan_*/scan_report.txt

# Decompile
apktool d -f -o ./decompiled $ARGUMENTS

# Find google-services.json
find ./decompiled -name "google-services.json"

# Search XML resources
grep -r "firebaseio.com\|appspot.com\|AIza" ./decompiled/res/

# Search assets (hybrid apps)
grep -r "firebaseio.com\|AIza" ./decompiled/assets/

# Test open signup
curl -s -X POST -H "Content-Type: application/json" \
  -d '{"email":"test@test.com","password":"Test123!","returnSecureToken":true}' \
  "https://identitytoolkit.googleapis.com/v1/accounts:signUp?key=API_KEY"

# Test anonymous auth
curl -s -X POST -H "Content-Type: application/json" \
  -d '{"returnSecureToken":true}' \
  "https://identitytoolkit.googleapis.com/v1/accounts:signUp?key=API_KEY"

# Realtime Database read
curl -s "https://PROJECT_ID.firebaseio.com/.json"

# Firestore read
curl -s "https://firestore.googleapis.com/v1/projects/PROJECT_ID/databases/(default)/documents"

# List bucket
curl -s "https://firebasestorage.googleapis.com/v0/b/PROJECT_ID.appspot.com/o"

curl -s -H "x-goog-api-key: API_KEY" \
  "https://firebaseremoteconfig.googleapis.com/v1/projects/PROJECT_ID/remoteConfig"

© trailofbits, CC-BY-SA-4.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 4 other files (references, assets) in plugins/firebase-apk-scanner/skills/firebase-apk-scanner of trailofbits/skills.

• SKILL.md
• agents/openai.yaml
• assets/trail-of-bits-mark.svg
• references/vulnerabilities.md
• scanner.sh

Open the folder on GitHubat commit 82fe822