{"id":"CVE-2026-26308","aliases":["BIT-envoy-2026-26308","EUVD-2026-10798","GHSA-ghc4-35x6-crw5"],"status":"published","title":"Envoy has an RBAC Header Validation Bypass via Multi-Value Header Concatenation","description":"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":{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00323,"percentile":0.25696,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-20","CWE-863"],"published":"2026-03-10T18:30:42Z","modified":"2026-10-28T11:09:55Z","fixes":[{"ecosystem":"Go","package":"github.com/envoyproxy/envoy","fixed_in":["1.37.1","1.36.5","1.35.9","1.34.13"],"sources":["ghsa","osv"]},{"ecosystem":"Bitnami","package":"envoy","fixed_in":["1.34.13","1.35.9","1.36.5","1.37.1"],"sources":["osv"]}],"affected":[{"source":"ghsa","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"1.37.0"},{"last_affected":"1.37.0"},{"fixed":"1.37.1"}]}],"versions":["1.37.0"]},{"source":"ghsa","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"1.36.0"},{"last_affected":"1.36.4"},{"fixed":"1.36.5"}]}]},{"source":"ghsa","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"1.35.0"},{"last_affected":"1.35.8"},{"fixed":"1.35.9"}]}]},{"source":"ghsa","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"1.34.12"},{"fixed":"1.34.13"}]}]},{"source":"osv","ecosystem":"Bitnami","package":"envoy","ranges":[{"type":"SEMVER","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"}]}]},{"source":"osv","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"SEMVER","events":[{"introduced":"1.37.0"},{"fixed":"1.37.1"}]}],"versions":["1.37.0"]},{"source":"osv","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"SEMVER","events":[{"introduced":"1.36.0"},{"fixed":"1.36.5"}]}]},{"source":"osv","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"SEMVER","events":[{"introduced":"1.35.0"},{"fixed":"1.35.9"}]}]},{"source":"osv","ecosystem":"Go","package":"github.com/envoyproxy/envoy","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.34.13"}]}]}],"products":[{"vendor":"envoyproxy","product":"envoy"}],"references":[{"url":"https://github.com/envoyproxy/envoy/security/advisories/GHSA-ghc4-35x6-crw5","tags":["x_refsource_CONFIRM","Exploit","Mitigation","Vendor Advisory","advisory","web"]},{"url":"https://github.com/envoyproxy/envoy/commit/b6ba0b2294b98484fb0ed8556897d1073cc27867","tags":["x_refsource_MISC","Patch","fix","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-26308","tags":["web","advisory"]},{"url":"https://github.com/advisories/GHSA-ghc4-35x6-crw5"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/26xxx/CVE-2026-26308.json","tags":["advisory"]},{"url":"https://github.com/envoyproxy/envoy","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-26308","title":"Envoy has an RBAC Header Validation Bypass via Multi-Value Header Concatenation","description":"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.","status":"published","published":"2026-03-10T19:01:28.062Z","modified":"2026-03-10T20:12:40.604Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N","level":"high","assessor":"cna"}],"cwes":["CWE-863"],"updated_at":"2026-11-02T13:38:32.13011Z"}],"euvd":[{"id":"EUVD-2026-10798","description":"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.","status":"published","published":"2026-03-10T19:01:28Z","modified":"2026-03-10T20:12:40Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N","level":"high"}],"updated_at":"2026-11-02T19:48:04.718931Z"}],"ghsa":[{"id":"GHSA-ghc4-35x6-crw5","title":"Envoy has RBAC Header Validation Bypass via Multi-Value Header Concatenation","description":"## 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—specifically \"Deny\" rules—by 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","status":"published","published":"2026-03-10T18:30:42Z","modified":"2026-04-13T17:29:35Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N","level":"high"}],"cwes":["CWE-20","CWE-863"],"updated_at":"2026-11-02T14:39:53.087746Z"}],"nvd":[{"id":"CVE-2026-26308","description":"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.","status":"published","published":"2026-03-10T20:16:35.707Z","modified":"2026-06-17T10:26:03.823Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N","level":"high","assessor":"secondary"},{"version":"3.1","score":8.2,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N","level":"high","assessor":"primary"}],"cwes":["CWE-863"],"updated_at":"2026-11-02T14:12:08.98071Z"}],"osv":[{"id":"CVE-2026-26308","title":"Envoy has an RBAC Header Validation Bypass via Multi-Value Header Concatenation","description":"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.","status":"published","published":"2026-03-10T19:01:28.062Z","modified":"2026-10-28T11:09:55.246949576Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N","level":"high"}],"cwes":["CWE-863"],"updated_at":"2026-11-02T15:44:59.80315Z"},{"id":"GHSA-ghc4-35x6-crw5","title":"Envoy has RBAC Header Validation Bypass via Multi-Value Header Concatenation","description":"## 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—specifically \"Deny\" rules—by 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","status":"published","published":"2026-03-10T18:30:42Z","modified":"2026-04-13T17:46:32.629556Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N","level":"high"}],"cwes":["CWE-20","CWE-863"],"updated_at":"2026-11-02T15:46:47.822182Z"},{"id":"BIT-envoy-2026-26308","title":"Envoy has an RBAC Header Validation Bypass via Multi-Value Header Concatenation","description":"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.","status":"published","published":"2026-03-12T08:39:41.078Z","modified":"2026-09-08T08:47:31.777064843Z","updated_at":"2026-11-02T15:28:29.563843Z"}]}}