# CVE-2026-82758: Auth bypass in ash authentication oauth2 server

> An unauthenticated attacker can register OAuth clients by exploiting a fail-open logic flaw in secret resolution, bypassing initial access token requirements.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 7 Sep 2026
- **Updated:** 8 Sep 2026
- **Also known as:** EEF-CVE-2026-82758, GHSA-fxc6-vp68-87pw

## What is CVE-2026-82758?

CVE-2026-82758 is a medium-severity authentication bypass vulnerability in ash-project ash_authentication_oauth2_server, published on 7 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Improper Authentication vulnerability in ash-project ash_authentication_oauth2_server allows an unauthenticated attacker to register OAuth clients even when Dynamic Client Registration is gated by an initial access token.

resolve_secret/3 in AshAuthentication.Oauth2Server (reached through __resolve_secret__!) treated any return other than {:ok, _} or :error from a configured {module, function, args} or 2-arity-function secret provider as a valid secret, wrapping nil, false, or "" as {:ok, value}. When the initial_access_token resolves to such an empty value, POST /oauth/register compares the presented bearer token against it and the comparison passes with no token supplied, so registration is open although it was configured closed. The same fail-open affected other resolved secrets such as signing_secret.

This issue affects ash_authentication_oauth2_server: from 0.1.0 before 0.3.1.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2026-82758?

1 open source package ship an affected version, including ash_authentication_oauth2_server.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `ash_authentication_oauth2_server` | Hex | From 0.1.0 | 0.3.1 |

## How do I fix CVE-2026-82758?

Upgrade ash_authentication_oauth2_server to 0.3.1 or later.

## Is CVE-2026-82758 being exploited?

There is no known exploitation of CVE-2026-82758 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-82758 and fix it if it is affected.

What it is: CVE-2026-82758 is a medium-severity authentication bypass vulnerability in ash-project ash_authentication_oauth2_server, published on 7 Sep 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-2026-82758 in the wild and no public exploit code.

Affected packages and fixed versions:
- ash_authentication_oauth2_server (Hex): affected from 0.1.0; fixed in 0.3.1

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-2026-82758/ (Markdown: https://insights.sbomify.com/CVE-2026-82758/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-82758
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-82758
- OSV: https://osv.dev/vulnerability/CVE-2026-82758

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-82758/
Summaries are generated and may contain mistakes; the official description above is the record.