# CVE-2026-82755: Information disclosure in ash authentication oauth2 server

> A shared HTTP cache may serve one tenant's OAuth metadata to another, causing clients to send secrets to the wrong endpoint or validate tokens incorrectly.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:L/SI:L/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-2026-82755, GHSA-crqf-7m54-4hgc

## What is CVE-2026-82755?

CVE-2026-82755 is a medium-severity 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

Use of Cache Containing Sensitive Information vulnerability in ash-project ash_authentication_oauth2_server allows a shared HTTP cache to serve one tenant's OAuth discovery metadata to another tenant's clients.

The RFC 8414 and RFC 9728 metadata endpoints in AshAuthentication.Phoenix.Oauth2Server.ProtocolRouter return tenant-specific values (issuer, authorization_endpoint, token_endpoint, jwks_uri) when a tenant is set, but sent them with Cache-Control: public, max-age=3600 and no Vary. When the tenant is derived from something other than the URL (a header or the Host) and a shared cache sits in front, the cache key is the URL alone, so a stored response for one tenant is served to another for up to an hour. Affected clients may then send authorization codes and secrets to the wrong tenant's token endpoint and validate tokens against the wrong keys.

This issue affects ash_authentication_oauth2_server: from 0.1.3 before 0.3.1.

Weakness: CWE-524 (Use of Cache Containing Sensitive Information)

## Which versions are affected by CVE-2026-82755?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `ash_authentication_oauth2_server` | Hex | From 0.1.3 | 0.3.1 |

## How do I fix CVE-2026-82755?

Upgrade ash_authentication_oauth2_server to 0.3.1 or later.

## Is CVE-2026-82755 being exploited?

There is no known exploitation of CVE-2026-82755 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-82755 and fix it if it is affected.

What it is: CVE-2026-82755 is a medium-severity 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-2026-82755 in the wild and no public exploit code.

Affected packages and fixed versions:
- ash_authentication_oauth2_server (Hex): affected from 0.1.3; 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-2026-82755/ (Markdown: https://insights.sbomify.com/CVE-2026-82755/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-82755
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-82755
- OSV: https://osv.dev/vulnerability/CVE-2026-82755

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-82755/
Summaries are generated and may contain mistakes; the official description above is the record.