EEF-CVE-2026-82755 CVE-2026-82755 GHSA-crqf-7m54-4hgc
ash_authentication_oauth2_server serves tenant-specific OAuth metadata as publicly cacheable without Vary, enabling cross-tenant confusion
- Severity
- 0.0 / 10
- Unknown · CVSS 4.0
- Exploit chance (EPSS)
- 0.66%
- Chance of exploitation in the next 30 days. Higher than 51.51% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-524 Use of Cache Containing Sensitive Information
- Fix
0.3.1- Upgrade ash_authentication_oauth2_server to this version or later
Description
Summary
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.
Configurations
Reachable only in a multi-tenant deployment where the tenant is derived from outside the request URL (a header or the Host) and a shared HTTP cache (CDN, reverse proxy) sits in front of the metadata endpoints.
Affected versions
Hex
| Package | Vulnerable | Fixed in |
|---|---|---|
| ash_authentication_oauth2_server | >= 0.1.3, < 0.3.1 |
0.3.1 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
ash_authentication_oauth2_server Hex → 0.3.1
- mix
{:ash_authentication_oauth2_server, "~> 0.3.1"} # then: mix deps.update ash_authentication_oauth2_server
Severity breakdown
CVSS 4.0 0.0
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
- Attack vector
- Network
- Attack complexity
- Low
- Attack requirements
- Present
- Privileges required
- None
- User interaction
- None
- Confidentiality (vulnerable system)
- Low
- Integrity (vulnerable system)
- None
- Availability (vulnerable system)
- None
- Confidentiality (subsequent systems)
- Low
- Integrity (subsequent systems)
- Low
- Availability (subsequent systems)
- None
Weakness
CWE-524: Use of Cache Containing Sensitive Information
The code uses a cache that contains sensitive information, but the cache can be read by an actor outside of the intended control sphere.
How to prevent it
- Architecture and Design: Protect information stored in cache.
- Architecture and Design: Do not store unnecessarily sensitive information in the cache.
- Architecture and Design: Consider using encryption in the cache.
References
Advisories
Fixes and patches
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| EEF-CVE-2026-82758 ash_authentication_oauth2_server treats an empty resolved secret as valid, opening the gated Dynamic Client Registration endpoint | Not rated yet | Also affects ash_authentication_oauth2_server |
| EEF-CVE-2026-82757 ash_authentication_oauth2_server CIMD fetcher classifies IPv4-in-IPv6 and site-local addresses as public, allowing SSRF | Not rated yet | Also affects ash_authentication_oauth2_server |
| EEF-CVE-2026-82756 ash_authentication_oauth2_server interpolates a tenant-derived value into the WWW-Authenticate challenge without escaping, allowing header parameter injection | Not rated yet | Also affects ash_authentication_oauth2_server |
| EEF-CVE-2026-82754 ash_authentication_oauth2_server aliases every protocol endpoint under /.well-known, bypassing path-scoped controls | Not rated yet | Also affects ash_authentication_oauth2_server |
| EEF-CVE-2026-82753 Unauthenticated authorize requests create unbounded, never-expiring CIMD client rows and cache entries in ash_authentication_oauth2_server | Not rated yet | Also affects ash_authentication_oauth2_server |
| GHSA-4w7w-5xrc-9h26 undici vulnerable to cache poisoning and cross-user disclosure via cross-origin redirects | Critical | Same weakness, CWE-524 |
| GHSA-5974-gfqc-wrcm Contao: Improper access control in the table access voter | Medium | Same weakness, CWE-524 |
| GHSA-935w-9g4m-p28p vLLM: Harmony tool continuations drop `cache_salt` — restoring a cross-tenant prefix-cache membership oracle | Low | Same weakness, CWE-524 |
Credits: Jonatan Männchen / EEF, Peter Ullrich, Zach Daniel / Ash Project
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