CVE-2026-82755 (GCVE-0-2026-82755)

Vulnerability from cvelistv5 – Published: 2026-09-07 22:28 – Updated: 2026-09-08 14:42
VLAI
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
6.3 (Medium)
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
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
EEF CNA under the mitre root
CNA scorecard A 97/100 over 343 records in the last 180 days details
References
Impacted 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:*:*:*:*:*:*:*:*
Create a notification for this product.
ash-project ash_authentication_oauth2_server Affected: 99de0a1cacb5ef667c4533278b7c81ca98c00231 , < 768d87f70e4e97ae1d2bf1606b5bf3f4d03f24a1 (git)
    cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*
Create a notification for this product.
Credits
Peter Ullrich Peter Ullrich Zach Daniel / Ash Project Jonatan Männchen / EEF
Show details on NVD website
To clipboard 

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                  "name": "\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.ProtocolRouter\u0027:call/2"
                }
              ],
              "repo": "https://github.com/ash-project/ash_authentication_oauth2_server",
              "vendor": "ash-project",
              "versions": [
                {
                  "lessThan": "0.3.1",
                  "status": "affected",
                  "version": "0.1.3",
                  "versionType": "semver"
                }
              ]
            },
            {
              "collectionURL": "https://github.com",
              "cpes": [
                "cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*"
              ],
              "defaultStatus": "unaffected",
              "modules": [
                "\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.ProtocolRouter\u0027"
              ],
              "packageName": "ash-project/ash_authentication_oauth2_server",
              "packageURL": "pkg:github/ash-project/ash_authentication_oauth2_server",
              "product": "ash_authentication_oauth2_server",
              "programFiles": [
                "lib/ash_authentication_phoenix/oauth2_server/protocol_router.ex"
              ],
              "programRoutines": [
                {
                  "name": "\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.ProtocolRouter\u0027:call/2"
                }
              ],
              "repo": "https://github.com/ash-project/ash_authentication_oauth2_server",
              "vendor": "ash-project",
              "versions": [
                {
                  "lessThan": "768d87f70e4e97ae1d2bf1606b5bf3f4d03f24a1",
                  "status": "affected",
                  "version": "99de0a1cacb5ef667c4533278b7c81ca98c00231",
                  "versionType": "git"
                }
              ]
            }
          ],
          "configurations": [
            {
              "lang": "en",
              "supportingMedia": [
                {
                  "base64": false,
                  "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."
                }
              ],
              "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."
            }
          ],
          "cpeApplicability": [
            {
              "nodes": [
                {
                  "cpeMatch": [
                    {
                      "criteria": "cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "0.3.1",
                      "versionStartIncluding": "0.1.3",
                      "vulnerable": true
                    }
                  ],
                  "negate": false,
                  "operator": "OR"
                }
              ],
              "operator": "AND"
            }
          ],
          "credits": [
            {
              "lang": "en",
              "type": "finder",
              "value": "Peter Ullrich"
            },
            {
              "lang": "en",
              "type": "reporter",
              "value": "Peter Ullrich"
            },
            {
              "lang": "en",
              "type": "remediation developer",
              "value": "Zach Daniel / Ash Project"
            },
            {
              "lang": "en",
              "type": "coordinator",
              "value": "Jonatan M\u00e4nnchen / EEF"
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "supportingMedia": [
                {
                  "base64": false,
                  "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."
                }
              ],
              "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."
            }
          ],
          "impacts": [
            {
              "capecId": "CAPEC-204",
              "descriptions": [
                {
                  "lang": "en",
                  "value": "CAPEC-204 Lifting Sensitive Data Embedded in Cache"
                }
              ]
            }
          ],
          "metrics": [
            {
              "cvssV4_0": {
                "Automatable": "NOT_DEFINED",
                "Recovery": "NOT_DEFINED",
                "Safety": "NOT_DEFINED",
                "attackComplexity": "LOW",
                "attackRequirements": "PRESENT",
                "attackVector": "NETWORK",
                "baseScore": 6.3,
                "baseSeverity": "MEDIUM",
                "privilegesRequired": "NONE",
                "providerUrgency": "NOT_DEFINED",
                "subAvailabilityImpact": "NONE",
                "subConfidentialityImpact": "LOW",
                "subIntegrityImpact": "LOW",
                "userInteraction": "NONE",
                "valueDensity": "NOT_DEFINED",
                "vectorString": "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",
                "version": "4.0",
                "vulnAvailabilityImpact": "NONE",
                "vulnConfidentialityImpact": "LOW",
                "vulnIntegrityImpact": "NONE",
                "vulnerabilityResponseEffort": "NOT_DEFINED"
              },
              "format": "CVSS",
              "scenarios": [
                {
                  "lang": "en",
                  "value": "GENERAL"
                }
              ]
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-524",
                  "description": "CWE-524 Use of Cache Containing Sensitive Information",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-09-07T22:28:24.500Z",
            "orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
            "shortName": "EEF"
          },
          "references": [
            {
              "tags": [
                "vendor-advisory",
                "related"
              ],
              "url": "https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-crqf-7m54-4hgc"
            },
            {
              "tags": [
                "related"
              ],
              "url": "https://cna.erlef.org/cves/CVE-2026-82755.html"
            },
            {
              "tags": [
                "related"
              ],
              "url": "https://osv.dev/vulnerability/EEF-CVE-2026-82755"
            },
            {
              "tags": [
                "patch"
              ],
              "url": "https://github.com/ash-project/ash_authentication_oauth2_server/commit/768d87f70e4e97ae1d2bf1606b5bf3f4d03f24a1"
            }
          ],
          "source": {
            "discovery": "EXTERNAL"
          },
          "title": "ash_authentication_oauth2_server serves tenant-specific OAuth metadata as publicly cacheable without Vary, enabling cross-tenant confusion"
        }
      },
      "cveMetadata": {
        "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
        "assignerShortName": "EEF",
        "cveId": "CVE-2026-82755",
        "datePublished": "2026-09-07T22:28:24.500Z",
        "dateReserved": "2026-08-31T01:00:10.817Z",
        "dateUpdated": "2026-09-08T14:42:17.718Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
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  • 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.
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  • 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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How durations are calculated

Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.

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