# CVE-2026-82757: ash_authentication_oauth2_server CIMD fetcher classifies IPv4-in-IPv6 and site-local addresses as public, allowing SSRF

> An SSRF vulnerability in the ash_authentication_oauth2_server library allows attackers to bypass IP restrictions and access internal services via crafted DNS records.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/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-2026-82757, GHSA-wprp-8gvj-p6cv

## What is CVE-2026-82757?

CVE-2026-82757 is a medium-severity server-side request forgery 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

Server-Side Request Forgery (SSRF) vulnerability in ash-project ash_authentication_oauth2_server allows an attacker who controls a client metadata URL and its DNS to make the server connect to internal or loopback addresses.

public_ip?/1 in AshAuthentication.Oauth2Server.CIMD.ReqFetcher enforces the outbound policy for CIMD metadata fetches. It classified several address forms as publicly routable that are not: IPv4-compatible ::/96 (for example ::127.0.0.1), SIIT IPv4-translated ::ffff:0:0:0/96, and deprecated site-local fec0::/10. A returned AAAA record in one of these ranges passed the policy, so a fetch pinned to that address reached space the policy was meant to block.

This issue affects ash_authentication_oauth2_server: from 0.3.0 before 0.3.1.

Weakness: CWE-918 (Server-Side Request Forgery)

## Which versions are affected by CVE-2026-82757?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `ash_authentication_oauth2_server` | Hex | From 0.3.0 | 0.3.1 |

## How do I fix CVE-2026-82757?

Upgrade ash_authentication_oauth2_server to 0.3.1 or later.

## Is CVE-2026-82757 being exploited?

There is no known exploitation of CVE-2026-82757 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-82757 and fix it if it is affected.

What it is: CVE-2026-82757 is a medium-severity server-side request forgery 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-2026-82757 in the wild and no public exploit code.

Affected packages and fixed versions:
- ash_authentication_oauth2_server (Hex): affected from 0.3.0; 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-2026-82757/ (Markdown: https://insights.sbomify.com/CVE-2026-82757/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-82757
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-82757
- OSV: https://osv.dev/vulnerability/CVE-2026-82757

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-82757/
Summaries are generated and may contain mistakes; the official description above is the record.