How the CVE Works:
The vulnerability resides in the `secure_redundant_execution` function within feldman_vss.py, which is designed to mitigate fault injection attacks by executing a function multiple times and comparing results. However, the implementation fails to provide adequate protection due to several critical flaws:
1. Lack of Isolation: Python’s execution environment cannot ensure true isolation between redundant executions, allowing fault injection to affect all executions simultaneously.
2. Timing Variations: The constant-time comparison implementation is vulnerable to timing attacks, as Python’s dynamic nature introduces timing discrepancies.
3. Insufficient Randomization: The randomized execution order and timing do not provide robust protection against advanced fault injection techniques.
4. Information Leakage: Error handling mechanisms may leak timing information about partial execution results, aiding attackers in refining their attacks.
These weaknesses enable attackers with physical access to bypass redundancy checks, extract secret polynomial coefficients, force acceptance of invalid shares, and manipulate commitment verification processes, ultimately compromising the Verifiable Secret Sharing scheme.
DailyCVE Form:
Platform: Python
Version: feldman_vss.py
Vulnerability: Fault Injection
Severity: Critical
Date: 2023-XX-XX
What Undercode Say:
Exploitation:
- Fault Injection Setup: Use hardware tools like voltage glitchers or clock glitchers to disrupt the execution environment.
- Timing Analysis: Measure execution times to identify discrepancies in redundant executions.
- Bypass Redundancy: Inject faults during specific execution phases to bypass redundancy checks.
- Extract Secrets: Target share generation or verification phases to extract polynomial coefficients.
- Manipulate Commitments: Force acceptance of fraudulent commitments by disrupting verification processes.
Protection:
- Reimplement in Rust: Rewrite security-critical functions in Rust to ensure memory safety and true isolation.
- Increase Redundancy: Modify the source code to increase the redundancy count from 5 to a higher number.
- Physical Security: Deploy the software in environments with strict physical security controls.
- Hardware Security Modules (HSMs): Use HSMs for key operations to prevent physical tampering.
- External Verification: Add external verification mechanisms for cryptographic operations.
Commands and Code:
1. Increase Redundancy:
Modify feldman_vss.py REDUNDANCY_COUNT = 10 Increase from 5 to 10
2. External Verification:
def external_verification(result): Implement external verification logic pass
3. Rust Implementation:
// Example Rust function for secure execution
fn secure_redundant_execution() -> Result<(), &'static str> {
// Implement secure execution logic
Ok(())
}
4. Timing Attack Mitigation:
import hmac def constant_time_compare(a, b): return hmac.compare_digest(a, b)
5. Deploy with Physical Security:
Use secure environments like AWS Nitro Enclaves aws nitro-enclaves deploy --config secure-config.yaml
6. HSM Integration:
Use HSM for key operations openssl engine pkcs11 -t
By addressing these vulnerabilities and implementing the suggested mitigations, the security of the Verifiable Secret Sharing scheme can be significantly enhanced.
References:
Reported By: https://github.com/advisories/GHSA-r8gc-qc2c-c7vh
Extra Source Hub:
Undercode
