CVE-2026-82755 (GCVE-0-2026-82755)
Vulnerability from cvelistv5 – Published: 2026-09-07 22:28 – Updated: 2026-09-08 14:42
VLAI
EPSS
VEX
Title
ash_authentication_oauth2_server serves tenant-specific OAuth metadata as publicly cacheable without Vary, enabling cross-tenant confusion
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.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-08 14:42 UTC
CWE
- CWE-524 - Use of Cache Containing Sensitive Information
Assigner
References
4 references
| URL | Tags |
|---|---|
| https://github.com/ash-project/ash_authentication… | vendor-advisoryrelated |
| https://cna.erlef.org/cves/CVE-2026-82755.html | related |
| https://osv.dev/vulnerability/EEF-CVE-2026-82755 | related |
| https://github.com/ash-project/ash_authentication… | patch |
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| ash-project | ash_authentication_oauth2_server |
Affected:
0.1.3 , < 0.3.1
(semver)
cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:* |
||
| ash-project | ash_authentication_oauth2_server |
Affected:
99de0a1cacb5ef667c4533278b7c81ca98c00231 , < 768d87f70e4e97ae1d2bf1606b5bf3f4d03f24a1
(git)
cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:* |
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\"\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.ProtocolRouter\u0027:call/2\"}]}], \"references\": [{\"url\": \"https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-crqf-7m54-4hgc\", \"tags\": [\"vendor-advisory\", \"related\"]}, {\"url\": \"https://cna.erlef.org/cves/CVE-2026-82755.html\", \"tags\": [\"related\"]}, {\"url\": \"https://osv.dev/vulnerability/EEF-CVE-2026-82755\", \"tags\": [\"related\"]}, {\"url\": \"https://github.com/ash-project/ash_authentication_oauth2_server/commit/768d87f70e4e97ae1d2bf1606b5bf3f4d03f24a1\", \"tags\": [\"patch\"]}], \"descriptions\": [{\"lang\": \"en\", \"value\": \"Use of Cache Containing Sensitive Information vulnerability in ash-project ash_authentication_oauth2_server allows a shared HTTP cache to serve one tenant\u0027s OAuth discovery metadata to another tenant\u0027s clients.\\n\\nThe 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\u0027s token endpoint and validate tokens against the wrong keys.\\n\\nThis issue affects ash_authentication_oauth2_server: from 0.1.3 before 0.3.1.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eUse of Cache Containing Sensitive Information vulnerability in ash-project ash_authentication_oauth2_server allows a shared HTTP cache to serve one tenant\u0027s OAuth discovery metadata to another tenant\u0027s clients.\u003c/p\u003e\\n\u003cp\u003eThe RFC 8414 and RFC 9728 metadata endpoints in \u003ccode\u003eAshAuthentication.Phoenix.Oauth2Server.ProtocolRouter\u003c/code\u003e return tenant-specific values (\u003ccode\u003eissuer\u003c/code\u003e, \u003ccode\u003eauthorization_endpoint\u003c/code\u003e, \u003ccode\u003etoken_endpoint\u003c/code\u003e, \u003ccode\u003ejwks_uri\u003c/code\u003e) when a tenant is set, but sent them with \u003ccode\u003eCache-Control: public, max-age=3600\u003c/code\u003e and no \u003ccode\u003eVary\u003c/code\u003e. When the tenant is derived from something other than the URL (a header or the \u003ccode\u003eHost\u003c/code\u003e) 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\u0027s token endpoint and validate tokens against the wrong keys.\u003c/p\u003e\\n\u003cp\u003eThis issue affects ash_authentication_oauth2_server: from 0.1.3 before 0.3.1.\u003c/p\u003e\", \"base64\": false}, {\"type\": \"text/markdown\", \"value\": \"Use of Cache Containing Sensitive Information vulnerability in ash-project ash_authentication_oauth2_server allows a shared HTTP cache to serve one tenant\u0027s OAuth discovery metadata to another tenant\u0027s clients.\\n\\nThe 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\u0027s token endpoint and validate tokens against the wrong keys.\\n\\nThis issue affects ash_authentication_oauth2_server: from 0.1.3 before 0.3.1.\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-524\", \"description\": \"CWE-524 Use of Cache Containing Sensitive Information\"}]}], \"configurations\": [{\"lang\": \"en\", \"value\": \"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.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eReachable only in a multi-tenant deployment where the tenant is derived from outside the request URL (a header or the \u003ccode\u003eHost\u003c/code\u003e) and a shared HTTP cache (CDN, reverse proxy) sits in front of the metadata endpoints.\u003c/p\u003e\", \"base64\": false}, {\"type\": \"text/markdown\", \"value\": \"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.\", \"base64\": false}]}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"0.3.1\", \"versionStartIncluding\": \"0.1.3\"}], \"operator\": \"OR\"}], \"operator\": \"AND\"}], \"providerMetadata\": {\"orgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"shortName\": \"EEF\", \"dateUpdated\": \"2026-09-07T22:28:24.500Z\"}}}",
"cveMetadata": "{\"cveId\": \"CVE-2026-82755\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-09-08T14:42:17.718Z\", \"dateReserved\": \"2026-08-31T01:00:10.817Z\", \"assignerOrgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"datePublished\": \"2026-09-07T22:28:24.500Z\", \"assignerShortName\": \"EEF\"}",
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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