Exploit Chains & CVEs

TL;DR

Yes, a chain of exploits can absolutely be represented by a single CVE (Common Vulnerabilities and Exposures) entry. However, it depends on how the vulnerabilities interact and whether they are considered part of a single attack scenario. The key is documenting the entire sequence clearly in the CVE description.

Understanding Exploit Chains

An exploit chain is when multiple vulnerabilities are used one after another to achieve a greater impact than any single vulnerability could on its own. Think of it like opening several locks to get into a room – each lock represents a separate vulnerability, but you need them all to succeed.

Can an Exploit Chain Get a CVE?

1. Single Attack Scenario: If the vulnerabilities are designed to be exploited together as part of a single attack path, they often qualify for a single CVE. This is especially true if one vulnerability enables another in the chain.
2. Independent Vulnerabilities: If the vulnerabilities can be exploited independently and don’t rely on each other, it’s more likely they will receive separate CVEs.

Steps to Determine if a Chain Warrants a Single CVE

1. Identify the Attack Path: Clearly map out how each vulnerability is used in sequence. What does vulnerability A allow, and how does that lead to exploiting vulnerability B?
2. Dependency Analysis: Is vulnerability B exploitable *without* first exploiting vulnerability A? If not, they are likely part of a chain.
3. Impact Assessment: Does the combined impact of the chain significantly exceed the impact of any single vulnerability? This strengthens the case for a single CVE.
4. Documentation is Key: Regardless of whether you get one or multiple CVEs, thorough documentation is crucial. The description should detail:
   • Each vulnerability involved
   • The order of exploitation
   • Any specific conditions required for the chain to work
   • Affected products and versions

Example Scenario

Let’s say you find:

• Vulnerability A: Cross-Site Scripting (XSS) in a login form.
• Vulnerability B: Session Fixation vulnerability.

An attacker could use the XSS to steal a user’s session cookie, then use that stolen cookie to exploit the session fixation vulnerability and gain access to the user’s account.

In this case, the XSS is *required* to make the Session Fixation practical. A single CVE would likely be appropriate, describing the entire attack chain: “XSS leading to Session Fixation for Account Takeover”.

Reporting Exploit Chains

1. Choose a Vendor/Program: Report to the relevant vendor or through a bug bounty program.
2. Detailed Report: Include all information from step 4 above (attack path, dependencies, impact).
3. Proof of Concept (PoC): Provide a PoC demonstrating the entire chain if possible. A simple script showing the XSS and then session takeover is ideal.

   # Example - Simplified PoC (Conceptual)

   # Step 1: Exploit XSS to steal cookie

   # Step 2: Use stolen cookie for Session Fixation

Resources

• CVE List: https://cve.mitre.org
• NIST National Vulnerability Database (NVD): https://nvd.nist.gov