# CVE-2026-22866: ENS DNSSEC Oracle Vulnerable to RSA Signature Forgery via Missing PKCS#1 v1.5 Padding Validation

> Attackers can forge RSA signatures to fraudulently claim domains under specific TLDs due to missing PKCS#1 v1.5 padding validation in ENS contracts.

- **Severity:** Low 2.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 25 Feb 2026
- **Updated:** 25 Feb 2026
- **Also known as:** GHSA-c6rr-7pmc-73wc

## What is CVE-2026-22866?

CVE-2026-22866 is a low-severity vulnerability in ensdomains ens-contracts, published on 25 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Ethereum Name Service (ENS) is a distributed, open, and extensible naming system based on the Ethereum blockchain. In versions 1.6.2 and prior, 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. Apatch was merged at commit c76c5ad0dc9de1c966443bd946fafc6351f87587. Possible workarounds include deploying the patched contracts and pointing DNSSECImpl.setAlgorithm to the deployed contract.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2026-22866?

2 open source packages ship an affected version, including @ensdomains/ens-contracts. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@ensdomains/ens-contracts` | npm | All versions to 1.6.2 | None |
| `@ensdomains/ens-contracts` | npm | All versions to 1.6.2 | None |

Products: Ens.domains Ethereum Name Service.

## How do I fix CVE-2026-22866?

No fix has been published for CVE-2026-22866 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-22866 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-22866 exists.

## Other vulnerabilities in ensdomains ens-contracts

- [CVE-2020-5232](https://insights.sbomify.com/CVE-2020-5232/): Ethereum Name Service - Malicious takeover of previously owned ENS names (high 8.7)
- [CVE-2023-38698](https://insights.sbomify.com/CVE-2023-38698/): .eth registrar controller can shorten the duration of registered names (medium 4.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-22866 and fix it if it is affected.

What it is: CVE-2026-22866 is a low-severity vulnerability in ensdomains ens-contracts, published on 25 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-22866 exists.

Affected packages and fixed versions:
- @ensdomains/ens-contracts (npm): affected all versions up to 1.6.2; no fix listed
- @ensdomains/ens-contracts (npm): affected all versions up to 1.6.2; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-22866/ (Markdown: https://insights.sbomify.com/CVE-2026-22866/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-22866
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-22866
- OSV: https://osv.dev/vulnerability/CVE-2026-22866

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-22866/
Summaries are generated and may contain mistakes; the official description above is the record.