Vulnerability-Lookup

CVE-2026-41059 (GCVE-0-2026-41059)

Vulnerability from cvelistv5 – Published: 2026-04-21 23:17 – Updated: 2026-04-22 13:13

Title

OAuth2 Proxy has an Authentication Bypass via Fragment Confusion in skip_auth_routes and skip_auth_regex

Summary

OAuth2 Proxy is a reverse proxy that provides authentication using OAuth2 providers. Versions 7.5.0 through 7.15.1 have a configuration-dependent authentication bypass. Deployments are affected when all of the following are true: Use of `skip_auth_routes` or the legacy `skip_auth_regex`; use of patterns that can be widened by attacker-controlled suffixes, such as `^/foo/.*/bar$` causing potential exposure of `/foo/secret`; and protected upstream applications that interpret `#` as a fragment delimiter or otherwise route the request to the protected base path. In deployments that rely on these settings, an unauthenticated attacker can send a crafted request containing a number sign in the path, including the browser-safe encoded form `%23`, so that OAuth2 Proxy matches a public allowlist rule while the backend serves a protected resource. Deployments that do not use these skip-auth options, or that only allow exact public paths with tightly scoped method and path rules, are not affected. A fix has been implemented in version 7.15.2 to normalize request paths more conservatively before skip-auth matching so fragment content does not influence allowlist decisions. Users who cannot upgrade immediately can reduce exposure by tightening or removing `skip_auth_routes` and `skip_auth_regex` rules, especially patterns that use broad wildcards across path segments. Recommended mitigations include replacing broad rules with exact, anchored public paths and explicit HTTP methods; rejecting requests whose path contains `%23` or `#` at the ingress, load balancer, or WAF level; and/or avoiding placing sensitive application paths behind broad `skip_auth_routes` rules.

Severity

8.2 (High)


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

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-04-22 13:13 UTC

CWE

CWE-288 - Authentication Bypass Using an Alternate Path or Channel

Assigner

GitHub_M mitre root

References

1 reference

URL	Tags
https://github.com/oauth2-proxy/oauth2-proxy/secu…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version	CPE status
oauth2-proxy	oauth2-proxy	Affected: >= 7.5.0, < 7.15.2	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-41059

Vulnerability from fkie_nvd - Published: 2026-04-22 00:16 - Updated: 2026-06-17 10:46

Severity

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

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-pxq7-h93f-9jrg	Vendor Advisory

Impacted products

	Vendor	Product	Version
	oauth2_proxy_project	oauth2_proxy	*

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "oauth2-proxy",
          "vendor": "oauth2-proxy",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 7.5.0, \u003c 7.15.2"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "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
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    }
  ],
  "id": "CVE-2026-41059",
  "lastModified": "2026-06-17T10:46:06.260",
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GHSA-PXQ7-H93F-9JRG

Vulnerability from github – Published: 2026-04-15 19:24 – Updated: 2026-04-24 20:40

Summary

OAuth2 Proxy has an Authentication Bypass via Fragment Confusion in skip_auth_routes and skip_auth_regex

Details

Impact

A configuration-dependent authentication bypass exists in OAuth2 Proxy.

Deployments are affected when all of the following are true:

Use of skip_auth_routes or the legacy skip_auth_regex * Use of patterns that can be widened by attacker-controlled suffixes, such as ^/foo/.*/bar$ causing potential exposure of /foo/secret * Protected upstream applications that interpret # as a fragment delimiter or otherwise route the request to the protected base path

In deployments that rely on these settings, an unauthenticated attacker can send a crafted request containing a number sign in the path, including the browser-safe encoded form %23, so that OAuth2 Proxy matches a public allowlist rule while the backend serves a protected resource.

Deployments that do not use these skip-auth options, or that only allow exact public paths with tightly scoped method and path rules, ARE NOT affected.

Patches

A fix has been implemented to normalize request paths more conservatively before skip-auth matching so fragment content does not influence allowlist decisions.

Released as part of v7.15.2

Workarounds

Users who cannot upgrade immediately can reduce exposure by tightening or removing skip_auth_routes and skip_auth_regex rules, especially patterns that use broad wildcards across path segments.

Recommended mitigations:

Replace broad rules with exact, anchored public paths and explicit HTTP methods
Reject requests whose path contains %23 or # at the ingress, load balancer, or WAF level
Avoid placing sensitive application paths behind broad skip_auth_routes rules

Severity

8.2 (High)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
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      "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-2026-41059"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-288"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-15T19:24:13Z",
    "nvd_published_at": "2026-04-22T00:16:27Z",
    "severity": "HIGH"
  },
  "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* Use of `skip_auth_routes` or the legacy `skip_auth_regex` * Use of patterns that can be widened by attacker-controlled suffixes,    such as `^/foo/.*/bar$` causing potential exposure of `/foo/secret` * Protected upstream applications that interpret `#` as a fragment delimiter    or otherwise route the request to the protected base path\n\nIn deployments that rely on these settings, an unauthenticated attacker can send a crafted request containing a number sign in the path, including the browser-safe encoded form `%23`, so that OAuth2 Proxy matches a public allowlist rule while the backend serves a protected resource.\n\nDeployments that do not use these skip-auth options, or that only allow exact public paths with tightly scoped method and path rules, **ARE NOT** affected.\n\n### Patches\n\nA fix has been implemented to normalize request paths more conservatively before skip-auth matching so fragment content does not influence allowlist decisions.\n\nReleased as part of `v7.15.2`\n\n### Workarounds\n\nUsers who cannot upgrade immediately can reduce exposure by tightening or removing `skip_auth_routes` and `skip_auth_regex` rules, especially patterns that use broad wildcards across path segments.\n\nRecommended mitigations:\n\n* Replace broad rules with exact, anchored public paths and explicit HTTP methods\n* Reject requests whose path contains `%23` or `#` at the ingress, load balancer, or WAF level\n* Avoid placing sensitive application paths behind broad `skip_auth_routes` rules",
  "id": "GHSA-pxq7-h93f-9jrg",
  "modified": "2026-04-24T20:40:56Z",
  "published": "2026-04-15T19:24:13Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-pxq7-h93f-9jrg"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-41059"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/oauth2-proxy/oauth2-proxy"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "OAuth2 Proxy has an Authentication Bypass via Fragment Confusion in skip_auth_routes and skip_auth_regex"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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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.
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Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-41059 (GCVE-0-2026-41059)

FKIE_CVE-2026-41059

GHSA-PXQ7-H93F-9JRG

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