Summary
ENS DNSSEC Oracle Vulnerable to RSA Signature Forgery via Missing PKCS#1 v1.5 Padding Validation
Affected contracts
| Contract | Address | Status |
|---|---|---|
| RSASHA256Algorithm | 0x9D1B5a639597f558bC37Cf81813724076c5C1e96 | Vulnerable |
| RSASHA1Algorithm | 0x6ca8624Bc207F043D140125486De0f7E624e37A1 | Vulnerable |
| DNSSECImpl | 0x0fc3152971714E5ed7723FAFa650F86A4BaF30C5 | Uses vulnerable algorithms |
| DNSRegistrar | 0xB32cB5677a7C971689228EC835800432B339bA2B | Attack entry point |
Workarounds
- Deploy the patched contracts
- Point DNSSECImpl.setAlgorithm to the deployed contract
Resources
https://github.com/ensdomains/ens-contracts-bug-62248-pr-509
Impact
The RSASHA256Algorithm and RSASHA1Algorithm contracts fail to validate PKCS#1 v1.5 padding structure when verifying RSA signatures. The contracts only check if the last 32 (or 20) bytes of the decrypted signature match the expected hash. This enables Bleichenbacher's 2006 signature forgery attack against DNS zones using RSA keys with low public exponents (e=3). Two ENS-supported TLDs (.cc and .name) use e=3 for their Key Signing Keys, allowing any domain under these TLDs to be fraudulently claimed on ENS without DNS ownership.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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The bug was reported via Immunefi with possible solutions. The patch was merged at https://github.com/ensdomains/ens-contracts/commit/c76c5ad0dc9de1c966443bd946fafc6351f87587
Frequently Asked Questions
- What is CVE-2026-22866? CVE-2026-22866 is a low-severity security vulnerability in @ensdomains/ens-contracts (npm), affecting versions <= 1.6.2. No fixed version is listed yet.
- Which versions of @ensdomains/ens-contracts are affected by CVE-2026-22866? @ensdomains/ens-contracts (npm) versions <= 1.6.2 is affected.
- Is there a fix for CVE-2026-22866? No fixed version is listed for CVE-2026-22866 yet. Monitor the advisory for updates and apply mitigations in the interim.
- Is CVE-2026-22866 exploitable, and should I be worried? Whether CVE-2026-22866 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-22866 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.