Severity: P2 (High), Memory corruption in signing hot path

Summary

Two struct destructors use sizeof(entire_struct) instead of sizeof(scalar_field) as the length for OPENSSL_cleanse(), causing a 320-byte heap overwrite past the intended 32 bytes. This corrupts STL container internals (std::vector, std::map) before their destructors run, causing undefined behavior on every signing session cleanup.

Locations

Instance 1: ecdsa_preprocessing_data

• File: include/cosigner/cmp_ecdsa_signing_service.h, line 85
• sizeof(k.data): 32 bytes
• sizeof(ecdsa_preprocessing_data): 352 bytes
• Overwrite: 320 bytes past k.data

~ecdsa_preprocessing_data() {OPENSSL_cleanse(k.data, sizeof(ecdsa_preprocessing_data));}

Instance 2: asymmetric_eddsa_signature_data

• File: include/cosigner/asymmetric_eddsa_cosigner_server.h, line 33

~asymmetric_eddsa_signature_data() {OPENSSL_cleanse(k.data, sizeof(asymmetric_eddsa_signature_data));}

Impact

• Fires on EVERY ECDSA and asymmetric EdDSA signing operation
• Zeroes STL container internals (vector pointers, map tree nodes) before destructors run
• Memory leak: heap allocations for vector/map data never freed
• UB per C++ standard: destructors operate on corrupted state
• In long-running MPC signing service: gradual memory exhaustion → DoS

PoC

poc/02-destructor-overflow-v2.cpp, demonstrates the 352 vs 32 mismatch and leaked allocations.

Remediation

~ecdsa_preprocessing_data() {
 OPENSSL_cleanse(&k, sizeof(elliptic_curve256_scalar_t) * 6 + sizeof(elliptic_curve256_point_t));
}

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Source · github.com/zionsworking/security-research-notebook · writeups/fireblocks/02-destructor-heap-overflow-P2.md