# CVE-2026-18918: OAuth 1.0 session-fixation chain via unauthenticated provisional-consumer registration and insecure v1_0Allowed default

> Attackers can bypass OAuth authorization checks in Eclipse Lyo by using unapproved provisional clients when 2-legged auth is enabled.

- **Severity:** Critical 9.1 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/AU:Y/R:U/V:C/RE:L/U:Red`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 28 Aug 2026
- **Updated:** 31 Aug 2026
- **Also known as:** GHSA-jhp3-fv3p-rj5c

## What is CVE-2026-18918?

CVE-2026-18918 is a critical authentication bypass vulnerability in Eclipse Lyo, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In Eclipse Lyo versions 2.0.0 to 7.0.0, OAuth server authorization checks can be bypassed when the 2-legged auth is supported by the server. In those cases, application that based their authz filters upon Lyo-provided `AbstractAdapterCredentialsFilter`, are vulnerable. An attacked can create a provisional trusted client (valid use-case) but then it can be used as a trusted client immediately without requiring the administrator approval to clear the provisional status. The 3-legged path requiring user interaction is not vulnerable and rejects provisional clients.

Weakness: CWE-863 (Incorrect Authorization)

## Which versions are affected by CVE-2026-18918?


## How do I fix CVE-2026-18918?

No fix has been published for CVE-2026-18918 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-18918 being exploited?

There is no known exploitation of CVE-2026-18918 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-18918 and fix it if it is affected.

What it is: CVE-2026-18918 is a critical authentication bypass vulnerability in Eclipse Lyo, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-18918 in the wild and no public exploit code.

Affected product: Eclipse Lyo. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-18918/ (Markdown: https://insights.sbomify.com/CVE-2026-18918/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18918
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18918
- OSV: https://osv.dev/vulnerability/CVE-2026-18918

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-18918/
Summaries are generated and may contain mistakes; the official description above is the record.