Executive brief
The Ethereum Name Service (ENS) DNSSEC Oracle contracts fail to properly validate RSA digital signatures used to secure domain name registrations. This flaw allows attackers to forge DNS signatures and fraudulently claim domain names under certain top-level domains (.cc and .name) without actually owning them, potentially enabling account takeover and DNS hijacking on the ENS platform.
Technical details
The RSASHA256Algorithm and RSASHA1Algorithm smart contracts contain a cryptographic validation flaw where they only verify the last 32 or 20 bytes of decrypted RSA signatures against the expected hash, omitting proper PKCS#1 v1.5 padding structure validation. This vulnerability enables Bleichenbacher's 2006 RSA signature forgery attack, which is particularly effective against RSA keys with low public exponents (e=3). Two ENS-supported TLDs (.cc and .name) use e=3 for their Key Signing Keys, allowing attackers to bypass DNS ownership verification and fraudulently register or transfer domains. The attack requires network access to DNS and no authentication; a patch has been merged to the ENS contracts repository. The affected contracts include RSASHA256Algorithm, RSASHA1Algorithm, DNSSECImpl, and DNSRegistrar.
Affected products
- ENS (Ethereum Name Service) ens-contracts 1.6.2 and earlier
Timeline
- 2026-02-25: disclosed
- 2026-02-25: patched: Patch merged at commit c76c5ad0dc9de1c966443bd946fafc6351f87587