Vulnerability-Lookup

CVE-2026-40575 (GCVE-0-2026-40575)

Vulnerability from cvelistv5 – Published: 2026-04-21 23:20 – Updated: 2026-07-15 01:00

Title

OAuth2 Proxy has an Authentication Bypass via X-Forwarded-Uri Header Spoofing

Summary

OAuth2 Proxy is a reverse proxy that provides authentication using OAuth2 providers. Versions 7.5.0 through 7.15.1 may trust a client-supplied `X-Forwarded-Uri` header when `--reverse-proxy` is enabled and `--skip-auth-regex` or `--skip-auth-route` is configured. An attacker can spoof this header so OAuth2 Proxy evaluates authentication and skip-auth rules against a different path than the one actually sent to the upstream application. This can result in an unauthenticated remote attacker bypassing authentication and accessing protected routes without a valid session. Impacted users are deployments that run oauth2-proxy with `--reverse-proxy` enabled and configure at least one `--skip-auth-regex` or `--skip-auth-route` rule. This issue is patched in `v7.15.2`. Some workarounds are available for those who cannot upgrade immediately. Strip any client-provided `X-Forwarded-Uri` header at the reverse proxy or load balancer level; explicitly overwrite `X-Forwarded-Uri` with the actual request URI before forwarding requests to OAuth2 Proxy; restrict direct client access to OAuth2 Proxy so it can only be reached through a trusted reverse proxy; and/or remove or narrow `--skip-auth-regex` / `--skip-auth-route` rules where possible. For nginx-based deployments, ensure `X-Forwarded-Uri` is set by nginx and not passed through from the client.

Severity

9.1 (Critical)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

8.7 (High)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N

SSVC

Exploitation: none Automatable: yes Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-04-22 14:15 UTC

CWE

CWE-290 - Authentication Bypass by Spoofing

Assigner

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/oauth2-proxy/oauth2-proxy/secu…	x_refsource_CONFIRM
https://access.redhat.com/security/cve/CVE-2026-40575	vdb-entryx_refsource_REDHAT
https://bugzilla.redhat.com/show_bug.cgi?id=2460449	issue-trackingx_refsource_REDHAT
https://security.access.redhat.com/data/csaf/v2/v…	x_sadp-csaf-vex

Impacted products

2 products

Vendor	Product	Version	CPE status
oauth2-proxy	oauth2-proxy	Affected: >= 7.5.0, < 7.15.2	guessed
Red Hat	Red Hat Ceph Storage 9	cpe:/a:redhat:ceph_storage:9

Show details on NVD website

JSON

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FKIE_CVE-2026-40575

Vulnerability from fkie_nvd - Published: 2026-04-22 00:16 - Updated: 2026-07-15 02:21

Severity

9.1 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
8.7 (High) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N

Summary

References

URL	Tags
security-advisories@github.com	https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-7x63-xv5r-3p2x	Vendor Advisory
0b0ca135-0b70-47e7-9f44-1890c2a1c46c	https://access.redhat.com/security/cve/CVE-2026-40575
0b0ca135-0b70-47e7-9f44-1890c2a1c46c	https://bugzilla.redhat.com/show_bug.cgi?id=2460449
0b0ca135-0b70-47e7-9f44-1890c2a1c46c	https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40575.json

Impacted products

	Vendor	Product	Version
	oauth2_proxy_project	oauth2_proxy	*

JSON

To clipboard

{
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      "affectedData": [
        {
          "product": "oauth2-proxy",
          "vendor": "oauth2-proxy",
          "versions": [
            {
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              "version": "\u003e= 7.5.0, \u003c 7.15.2"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    },
    {
      "affectedData": [
        {
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "cpes": [
            "cpe:/a:redhat:ceph_storage:9"
          ],
          "defaultStatus": "affected",
          "packageName": "rhceph/oauth2-proxy-rhel9",
          "product": "Red Hat Ceph Storage 9",
          "vendor": "Red Hat"
        }
      ],
      "source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:oauth2_proxy_project:oauth2_proxy:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "03587628-7B66-41FF-B89D-DF35A5134CD7",
              "versionEndExcluding": "7.15.2",
              "versionStartIncluding": "7.5.0",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "OAuth2 Proxy is a reverse proxy that provides authentication using OAuth2 providers. Versions 7.5.0 through 7.15.1 may trust a client-supplied `X-Forwarded-Uri` header when `--reverse-proxy` is enabled and `--skip-auth-regex` or `--skip-auth-route` is configured. An attacker can spoof this header so OAuth2 Proxy evaluates authentication and skip-auth rules against a different path than the one actually sent to the upstream application. This can result in an unauthenticated remote attacker bypassing authentication and accessing protected routes without a valid session. Impacted users are deployments that run oauth2-proxy with `--reverse-proxy` enabled and configure at least one `--skip-auth-regex` or `--skip-auth-route` rule. This issue is patched in `v7.15.2`. Some workarounds are available for those who cannot upgrade immediately. Strip any client-provided `X-Forwarded-Uri` header at the reverse proxy or load balancer level; explicitly overwrite `X-Forwarded-Uri` with the actual request URI before forwarding requests to OAuth2 Proxy; restrict direct client access to OAuth2 Proxy so it can only be reached through a trusted reverse proxy; and/or remove or narrow `--skip-auth-regex` / `--skip-auth-route` rules where possible. For nginx-based deployments, ensure `X-Forwarded-Uri` is set by nginx and not passed through from the client."
    }
  ],
  "id": "CVE-2026-40575",
  "lastModified": "2026-07-15T02:21:07.520",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 9.1,
          "baseSeverity": "CRITICAL",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 5.2,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      },
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 8.7,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "CHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N",
          "version": "3.1"
        },
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        "impactScore": 5.8,
        "source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-40575",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-04-22T14:15:18.160877Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-04-22T00:16:27.817",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Vendor Advisory"
      ],
      "url": "https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-7x63-xv5r-3p2x"
    },
    {
      "source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c",
      "url": "https://access.redhat.com/security/cve/CVE-2026-40575"
    },
    {
      "source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c",
      "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2460449"
    },
    {
      "source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40575.json"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-290"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    },
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-290"
        }
      ],
      "source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c",
      "type": "Secondary"
    }
  ]
}

GHSA-7X63-XV5R-3P2X

Vulnerability from github – Published: 2026-04-15 19:21 – Updated: 2026-07-21 13:50

Summary

OAuth2 Proxy has an Authentication Bypass via X-Forwarded-Uri Header Spoofing

Details

Impact

A configuration-dependent authentication bypass exists in OAuth2 Proxy.

Deployments are affected when all of the following are true:

OAuth2 Proxy is configured with --reverse-proxy
and at least one rule is defined with --skip_auth_routes or the legacy --skip-auth-regex

OAuth2 Proxy may trust a client-supplied X-Forwarded-Uri header when --reverse-proxy is enabled and --skip-auth-route or --skip-auth-regex is configured. An attacker can spoof this header so OAuth2 Proxy evaluates authentication and skip-auth rules against a different path than the one actually sent to the upstream application.

This can result in an unauthenticated remote attacker bypassing authentication and accessing protected routes without a valid session.

Patches

This issue is addressed as part of the newly introduced --trusted-proxy-ip flag in v7.15.2. If you leave it unset, OAuth2 Proxy will continue to trust ALL source IPs (0.0.0.0/0) for backwards compatibility, which means a client may still be able to spoof forwarded headers. Therefore after upgrading we urge you to use the new --trusted-proxy-ip flag to set the IPs or CIDR ranges of the reverse proxies that are allowed to send X-Forwarded-* headers and furthermore implement the mitigation steps outlined below to properly configure your load balancer infrastructure.

Mitigation

Strip any client-provided X-Forwarded-Uri header at the reverse proxy or load balancer level
Explicitly overwrite X-Forwarded-Uri with the actual request URI before forwarding requests to OAuth2 Proxy

Example nginx mitigation for the auth subrequest: ``` location /internal-auth/ { internal; # Ensure external users can't access this path

  # Make sure the OAuth2 Proxy knows where the original request came from.
  proxy_set_header Host       $host;
  proxy_set_header X-Real-IP  $remote_addr;
  # set the value to the actual $request_uri and therefore strip any user provided X-Forwarded-Uri
  proxy_set_header X-Forwarded-Uri $request_uri;

  proxy_pass http://oauth2-proxy:4180/;
}

`` - Restrict direct client access to OAuth2 Proxy so it can only be reached through a trusted reverse proxy - Remove or narrow--skip-auth-route/--skip-auth-regex` rules where possible

Severity

9.1 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/oauth2-proxy/oauth2-proxy/v7"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "7.5.0"
            },
            {
              "fixed": "7.15.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-40575"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-290"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-15T19:21:06Z",
    "nvd_published_at": "2026-04-22T00:16:27Z",
    "severity": "CRITICAL"
  },
  "details": "### Impact\n\nA configuration-dependent authentication bypass exists in OAuth2 Proxy.\n\nDeployments are affected when all of the following are true:\n\n* OAuth2 Proxy is configured with `--reverse-proxy`\n* and at least one rule is defined with `--skip_auth_routes` or the legacy `--skip-auth-regex`\n\nOAuth2 Proxy may trust a client-supplied `X-Forwarded-Uri` header when `--reverse-proxy` is enabled and `--skip-auth-route` or `--skip-auth-regex` is configured. An attacker can spoof this header so OAuth2 Proxy evaluates authentication and skip-auth rules against a different path than the one actually sent to the upstream application.\n\nThis can result in an unauthenticated remote attacker bypassing authentication and accessing protected routes without a valid session.\n\n\n### Patches\nThis issue is addressed as part of the newly introduced `--trusted-proxy-ip` flag in `v7.15.2`. If you leave it unset, OAuth2 Proxy will **continue to trust ALL** source IPs (0.0.0.0/0) for backwards compatibility, which means a client may still be able to spoof forwarded headers. Therefore after upgrading we urge you to use the new `--trusted-proxy-ip` flag to set the IPs or CIDR ranges of the reverse proxies that are allowed to send `X-Forwarded-*` headers and furthermore implement the mitigation steps outlined below to properly configure your load balancer infrastructure.\n\n### Mitigation\n\n- Strip any client-provided `X-Forwarded-Uri` header at the reverse proxy or load balancer level\n- Explicitly overwrite `X-Forwarded-Uri` with the actual request URI before forwarding requests to OAuth2 Proxy\n\n  Example nginx mitigation for the auth subrequest:\n  ```\n    location /internal-auth/ {\n      internal; # Ensure external users can\u0027t access this path\n  \n      # Make sure the OAuth2 Proxy knows where the original request came from.\n      proxy_set_header Host       $host;\n      proxy_set_header X-Real-IP  $remote_addr;\n      # set the value to the actual $request_uri and therefore strip any user provided X-Forwarded-Uri\n      proxy_set_header X-Forwarded-Uri $request_uri;\n  \n      proxy_pass http://oauth2-proxy:4180/;\n    }\n  ```\n- Restrict direct client access to OAuth2 Proxy so it can only be reached through a trusted reverse proxy\n- Remove or narrow `--skip-auth-route` / `--skip-auth-regex` rules where possible",
  "id": "GHSA-7x63-xv5r-3p2x",
  "modified": "2026-07-21T13:50:15Z",
  "published": "2026-04-15T19:21:06Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-7x63-xv5r-3p2x"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-40575"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/security/cve/CVE-2026-40575"
    },
    {
      "type": "WEB",
      "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2460449"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/oauth2-proxy/oauth2-proxy"
    },
    {
      "type": "WEB",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40575.json"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "OAuth2 Proxy has an Authentication Bypass via X-Forwarded-Uri Header Spoofing"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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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.

Detection rules are retrieved from Rulezet.

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.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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Action not permitted

CVE-2026-40575 (GCVE-0-2026-40575)

FKIE_CVE-2026-40575

GHSA-7X63-XV5R-3P2X

Impact

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