CVE-2025-30147 - The curious case of subgroup check on Besu

The Ethereum Foundation highlights a major consensus flaw—CVE-2025-30147—in Besu version 25.2.2, a popular Ethereum client. The vulnerability stems from an incomplete elliptic curve verification process, exposing the network to potential cryptographic attacks and emphasizing the importance of robust consensus checks in multi-client blockchain ecosystems.

Key Ideas

Improper Curve Validation: Besu skipped the is_on_curve check for bn254 curve points in precompiled contracts, allowing crafted points to pass subgroup checks while being cryptographically invalid.
Security and Coordination Implications: Such discrepancies can lead to chain splits if clients disagree on transaction validity. The vulnerability was identified during the Pectra Audit Competition and patched in version 25.3.0.
Developer Takeaway: Builders should always ensure both is_on_curve and is_in_subgroup checks are properly implemented and validated. Participating in audits and bounty programs is essential for hardening blockchain infrastructure against subtle but critical flaws.