Vulnerability-Lookup

CVE-2026-26308 (GCVE-0-2026-26308)

Vulnerability from cvelistv5 – Published: 2026-03-10 19:01 – Updated: 2026-03-10 20:12

Title

Envoy has an RBAC Header Validation Bypass via Multi-Value Header Concatenation

Summary

Envoy is a high-performance edge/middle/service proxy. Prior to 1.37.1, 1.36.5, 1.35.8, and 1.34.13, the Envoy RBAC (Role-Based Access Control) filter contains a logic vulnerability in how it validates HTTP headers when multiple values are present for the same header name. Instead of validating each header value individually, Envoy concatenates all values into a single comma-separated string. This behavior allows attackers to bypass RBAC policies—specifically "Deny" rules—by sending duplicate headers, effectively obscuring the malicious value from exact-match mechanisms. This vulnerability is fixed in 1.37.1, 1.36.5, 1.35.8, and 1.34.13.

Severity ?

7.5 (High)


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

CWE

CWE-863 - Incorrect Authorization

Assigner

GitHub_M

References

URL

Tags

	https://github.com/envoyproxy/envoy/security/advi…	x_refsource_CONFIRM
	https://github.com/envoyproxy/envoy/commit/b6ba0b…	x_refsource_MISC

Impacted products

	Vendor	Product	Version
	envoyproxy	envoy	Affected: >= 1.37.0, < 1.37.1 Affected: >= 1.36.0, < 1.36.5 Affected: >= 1.35.0, < 1.35.9 Affected: < 1.34.13

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JSON

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GHSA-GHC4-35X6-CRW5

Vulnerability from github – Published: 2026-03-10 18:30 – Updated: 2026-03-10 22:24

Summary

Envoy has RBAC Header Validation Bypass via Multi-Value Header Concatenation

Details

1. Summary

The Envoy RBAC (Role-Based Access Control) filter contains a logic vulnerability in how it validates HTTP headers when multiple values are present for the same header name. Instead of validating each header value individually, Envoy concatenates all values into a single comma-separated string. This behavior allows attackers to bypass RBAC policies—specifically "Deny" rules—by sending duplicate headers, effectively obscuring the malicious value from exact-match mechanisms.

2. Attack Scenario

Consider an environment where an administrator wants to block external access to internal resources using a specific header flag.

Configuration

The Envoy proxy is configured with a Deny rule to reject requests containing the header internal: true. * Rule Type: Exact Match * Target: internal header must not equal true.

The Bypass Logic

Standard Request (Blocked):
- Input: internal: true
- Envoy Processing: Sees string "true".
- Result: Match found. Request Denied.
Exploit Request (Bypassed):
- Input: http internal: true internal: true
- Envoy Processing: Concatenates values into "true,true".
- Matcher Evaluation: Does "true,true" equal "true"? No.
- Result: The Deny rule fails to trigger. Request Allowed.

3. Implications

RBAC Bypass: Remote attackers can bypass configured access controls.
Unauthorized Access: Sensitive internal resources or administrative endpoints protected by header-based Deny rules become accessible.
Risk: High, particularly for deployments relying on "Exact Match" strategies for security blocking.

4. Reproduction Steps

To verify this vulnerability:

Deploy Envoy: Configure an instance with an RBAC Deny rule that performs an exact match on a specific header (e.g., internal: true).
Baseline Test: Send a request containing the header internal: true.
- Observation: Envoy blocks this request (HTTP 403).
Exploit Test: Send a second request containing the same header twice: http GET /restricted-resource HTTP/1.1 Host: example.com internal: true internal: true
- Observation: Envoy allows the request, granting access to the resource.

6. Recommendations

Fix Header Validation Logic: Modify the RBAC filter to validate each header value instance individually. Avoid relying on the concatenated string output of getAllOfHeaderAsString() for security-critical matching unless the matcher is explicitly designed to parse comma-separated lists.

** Examine the DENY role to use a Regex style fix.

Credit: Dor Konis

Severity ?

7.5 (High)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/envoyproxy/envoy"
      },
      "versions": [
        "1.37.0"
      ]
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        "name": "github.com/envoyproxy/envoy"
      },
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          "events": [
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              "introduced": "1.36.0"
            },
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            }
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          "type": "ECOSYSTEM"
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    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/envoyproxy/envoy"
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      "ranges": [
        {
          "events": [
            {
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              "last_affected": "1.35.8"
            }
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          "type": "ECOSYSTEM"
        }
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    },
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      "package": {
        "ecosystem": "Go",
        "name": "github.com/envoyproxy/envoy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "1.34.12"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-26308"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20",
      "CWE-863"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-10T18:30:42Z",
    "nvd_published_at": "2026-03-10T20:16:35Z",
    "severity": "HIGH"
  },
  "details": "## 1. Summary\nThe Envoy RBAC (Role-Based Access Control) filter contains a logic vulnerability in how it validates HTTP headers when multiple values are present for the same header name. Instead of validating each header value individually, Envoy concatenates all values into a single comma-separated string. This behavior allows attackers to bypass RBAC policies\u2014specifically \"Deny\" rules\u2014by sending duplicate headers, effectively obscuring the malicious value from exact-match mechanisms.\n\n## 2. Attack Scenario\nConsider an environment where an administrator wants to block external access to internal resources using a specific header flag.\n\n### Configuration\nThe Envoy proxy is configured with a **Deny** rule to reject requests containing the header `internal: true`.\n* **Rule Type:** Exact Match\n* **Target:** `internal` header must not equal `true`.\n\n### The Bypass Logic\n1.  **Standard Request (Blocked):**\n    * **Input:** `internal: true`\n    * **Envoy Processing:** Sees string `\"true\"`.\n    * **Result:** Match found. **Request Denied.**\n\n2.  **Exploit Request (Bypassed):**\n    * **Input:**\n        ```http\n        internal: true\n        internal: true\n        ```\n    * **Envoy Processing:** Concatenates values into `\"true,true\"`.\n    * **Matcher Evaluation:** Does `\"true,true\"` equal `\"true\"`? **No.**\n    * **Result:** The Deny rule fails to trigger. **Request Allowed.**\n\n## 3. Implications\n* **RBAC Bypass:** Remote attackers can bypass configured access controls.\n* **Unauthorized Access:** Sensitive internal resources or administrative endpoints protected by header-based Deny rules become accessible.\n* **Risk:** High, particularly for deployments relying on \"Exact Match\" strategies for security blocking.\n\n## 4. Reproduction Steps\nTo verify this vulnerability:\n\n1.  **Deploy Envoy:** Configure an instance with an RBAC **Deny** rule that performs an **exact match** on a specific header (e.g., `internal: true`).\n2.  **Baseline Test:** Send a request containing the header `internal: true`.\n    * *Observation:* Envoy blocks this request (HTTP 403).\n3.  **Exploit Test:** Send a second request containing the same header twice:\n    ```http\n    GET /restricted-resource HTTP/1.1\n    Host: example.com\n    internal: true\n    internal: true\n    ```\n    * *Observation:* Envoy allows the request, granting access to the resource.\n\n## 6. Recommendations\n**Fix Header Validation Logic:**\nModify the RBAC filter to validate each header value instance individually. Avoid relying on the concatenated string output of `getAllOfHeaderAsString()` for security-critical matching unless the matcher is explicitly designed to parse comma-separated lists.\n\n** Examine the DENY role to use a Regex style fix.\n\n**Credit:** Dor Konis",
  "id": "GHSA-ghc4-35x6-crw5",
  "modified": "2026-03-10T22:24:17Z",
  "published": "2026-03-10T18:30:42Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/envoyproxy/envoy/security/advisories/GHSA-ghc4-35x6-crw5"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-26308"
    },
    {
      "type": "WEB",
      "url": "https://github.com/envoyproxy/envoy/commit/b6ba0b2294b98484fb0ed8556897d1073cc27867"
    },
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      "type": "PACKAGE",
      "url": "https://github.com/envoyproxy/envoy"
    }
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  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Envoy has RBAC Header Validation Bypass via Multi-Value Header Concatenation"
}

FKIE_CVE-2026-26308

Vulnerability from fkie_nvd - Published: 2026-03-10 20:16 - Updated: 2026-03-11 16:23

Severity ?

7.5 (High) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N
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/envoyproxy/envoy/commit/b6ba0b2294b98484fb0ed8556897d1073cc27867	Patch
	security-advisories@github.com	https://github.com/envoyproxy/envoy/security/advisories/GHSA-ghc4-35x6-crw5	Exploit, Mitigation, Vendor Advisory

Impacted products

Vendor	Product	Version
envoyproxy	envoy	*
envoyproxy	envoy	*
envoyproxy	envoy	*
envoyproxy	envoy	1.37.0

JSON

To clipboard

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            },
            {
              "criteria": "cpe:2.3:a:envoyproxy:envoy:1.37.0:*:*:*:*:*:*:*",
              "matchCriteriaId": "C5266F62-E0D2-4525-90B6-65921EE14F79",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Envoy is a high-performance edge/middle/service proxy. Prior to 1.37.1, 1.36.5, 1.35.8, and 1.34.13, the Envoy RBAC (Role-Based Access Control) filter contains a logic vulnerability in how it validates HTTP headers when multiple values are present for the same header name. Instead of validating each header value individually, Envoy concatenates all values into a single comma-separated string. This behavior allows attackers to bypass RBAC policies\u2014specifically \"Deny\" rules\u2014by sending duplicate headers, effectively obscuring the malicious value from exact-match mechanisms. This vulnerability is fixed in 1.37.1, 1.36.5, 1.35.8, and 1.34.13."
    },
    {
      "lang": "es",
      "value": "Envoy es un proxy de alto rendimiento de borde/intermedio/servicio. Antes de 1.37.1, 1.36.5, 1.35.8 y 1.34.13, el filtro RBAC (control de acceso basado en roles) de Envoy contiene una vulnerabilidad l\u00f3gica en c\u00f3mo valida los encabezados HTTP cuando hay m\u00faltiples valores presentes para el mismo nombre de encabezado. En lugar de validar cada valor de encabezado individualmente, Envoy concatena todos los valores en una \u00fanica cadena separada por comas. Este comportamiento permite a los atacantes eludir las pol\u00edticas RBAC \u2014espec\u00edficamente las reglas de \u0027Denegar\u0027\u2014 enviando encabezados duplicados, ocultando eficazmente el valor malicioso de los mecanismos de coincidencia exacta. Esta vulnerabilidad est\u00e1 corregida en 1.37.1, 1.36.5, 1.35.8 y 1.34.13."
    }
  ],
  "id": "CVE-2026-26308",
  "lastModified": "2026-03-11T16:23:23.090",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "LOW",
          "privilegesRequired": "NONE",
          "scope": "CHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.2,
        "impactScore": 4.7,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      },
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 8.2,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "LOW",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 4.2,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ]
  },
  "published": "2026-03-10T20:16:35.707",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Patch"
      ],
      "url": "https://github.com/envoyproxy/envoy/commit/b6ba0b2294b98484fb0ed8556897d1073cc27867"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Exploit",
        "Mitigation",
        "Vendor Advisory"
      ],
      "url": "https://github.com/envoyproxy/envoy/security/advisories/GHSA-ghc4-35x6-crw5"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-863"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

bit-envoy-2026-26308

Vulnerability from bitnami_vulndb

Published

2026-03-12 08:39

Modified

2026-03-12 09:10

Summary

Envoy has an RBAC Header Validation Bypass via Multi-Value Header Concatenation

Details

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "Bitnami",
        "name": "envoy",
        "purl": "pkg:bitnami/envoy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.34.13"
            },
            {
              "introduced": "1.35.0"
            },
            {
              "fixed": "1.35.9"
            },
            {
              "introduced": "1.36.0"
            },
            {
              "fixed": "1.36.5"
            },
            {
              "introduced": "1.37.0"
            },
            {
              "fixed": "1.37.1"
            }
          ],
          "type": "SEMVER"
        }
      ],
      "severity": [
        {
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N",
          "type": "CVSS_V3"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-26308"
  ],
  "database_specific": {
    "cpes": [
      "cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:go:*:*"
    ],
    "severity": "High"
  },
  "details": "Envoy is a high-performance edge/middle/service proxy. Prior to 1.37.1, 1.36.5, 1.35.8, and 1.34.13, the Envoy RBAC (Role-Based Access Control) filter contains a logic vulnerability in how it validates HTTP headers when multiple values are present for the same header name. Instead of validating each header value individually, Envoy concatenates all values into a single comma-separated string. This behavior allows attackers to bypass RBAC policies\u2014specifically \"Deny\" rules\u2014by sending duplicate headers, effectively obscuring the malicious value from exact-match mechanisms. This vulnerability is fixed in 1.37.1, 1.36.5, 1.35.8, and 1.34.13.",
  "id": "BIT-envoy-2026-26308",
  "modified": "2026-03-12T09:10:07.191Z",
  "published": "2026-03-12T08:39:41.078Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/envoyproxy/envoy/commit/b6ba0b2294b98484fb0ed8556897d1073cc27867"
    },
    {
      "type": "WEB",
      "url": "https://github.com/envoyproxy/envoy/security/advisories/GHSA-ghc4-35x6-crw5"
    },
    {
      "type": "WEB",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-26308"
    }
  ],
  "schema_version": "1.6.2",
  "summary": "Envoy has an RBAC Header Validation Bypass via Multi-Value Header Concatenation"
}

Sightings

Author	Source	Type	Date

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.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2026-26308 (GCVE-0-2026-26308)

GHSA-GHC4-35X6-CRW5

1. Summary

2. Attack Scenario

Configuration

The Bypass Logic

3. Implications

4. Reproduction Steps

6. Recommendations

FKIE_CVE-2026-26308

bit-envoy-2026-26308

Vulnerability from bitnami_vulndb

Tags

Sightings

Nomenclature