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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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
Which versions are affected by CVE-2026-82757?
1 open source package ship an affected version, including ash_authentication_oauth2_server.
| Package | 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.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-82757 being exploited?
There is no known exploitation of CVE-2026-82757 in the wild and no public exploit code.
Sources
Also known as EEF-CVE-2026-82757, GHSA-wprp-8gvj-p6cv.