{ "document": { "category": "csaf_base", "csaf_version": "2.0", "distribution": { "tlp": { "label": "WHITE" } }, "lang": "en", "notes": [ { "category": "legal_disclaimer", "text": "The Netherlands Cyber Security Center (henceforth: NCSC-NL) maintains this portal to enhance access to its information and vulnerabilities. The use of this information is subject to the following terms and conditions:\n\nThe vulnerabilities disclosed in this portal are gathered by NCSC-NL from a variety of open sources, which the user can retrieve from other platforms. NCSC-NL makes every reasonable effort to ensure that the content of this portal is kept up to date, and that it is accurate and complete. Nevertheless, NCSC-NL cannot entirely rule out the possibility of errors, and therefore cannot give any warranty in respect of its completeness, accuracy or real-time keeping up-to-date. NCSC-NL does not control nor guarantee the accuracy, relevance, timeliness or completeness of information obtained from these external sources. The vulnerabilities disclosed in this portal are intended solely for the convenience of professional parties to take appropriate measures to manage the risks posed to the cybersecurity. No rights can be derived from the information provided therein.\n\nNCSC-NL and the Kingdom of the Netherlands assume no legal liability or responsibility for any damage resulting from either the use or inability of use of the vulnerabilities disclosed in this portal. This includes damage resulting from the inaccuracy of incompleteness of the information contained in it.\nThe information on this page is subject to Dutch law. All disputes related to or arising from the use of this portal regarding the disclosure of vulnerabilities will be submitted to the competent court in The Hague. This choice of means also applies to the court in summary proceedings." } ], "publisher": { "category": "coordinator", "contact_details": "cert@ncsc.nl", "name": "National Cyber Security Centre", "namespace": "https://www.ncsc.nl/" }, "title": "CVE-2026-33433", "tracking": { "current_release_date": "2026-04-03T17:26:05.818570Z", "generator": { "date": "2026-02-17T15:00:00Z", "engine": { "name": "V.E.L.M.A", "version": "1.7" } }, "id": "CVE-2026-33433", "initial_release_date": "2026-03-27T19:43:27.282254Z", "revision_history": [ { "date": "2026-03-27T19:43:27.282254Z", "number": "1", "summary": "CVE created.| Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| Products created (2).| Products connected (1).| References created (4).| CWES updated (1)." }, { "date": "2026-03-27T19:43:43.668472Z", "number": "2", "summary": "NCSC Score created." }, { "date": "2026-03-27T19:44:39.971924Z", "number": "3", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (4).| CWES updated (1)." }, { "date": "2026-03-27T19:44:42.805749Z", "number": "4", "summary": "NCSC Score updated." }, { "date": "2026-03-27T20:47:57.170248Z", "number": "5", "summary": "NCSC Score updated." }, { "date": "2026-03-27T21:35:06.782605Z", "number": "6", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (6).| CWES updated (1)." }, { "date": "2026-03-27T21:35:19.286804Z", "number": "7", "summary": "NCSC Score updated." }, { "date": "2026-03-28T12:28:30.649927Z", "number": "8", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| Products connected (2).| Product Identifiers created (1).| Product Remediations created (2).| References created (6).| CWES updated (1).| Vendor_assessment created." }, { "date": "2026-03-28T12:28:33.989298Z", "number": "9", "summary": "NCSC Score updated." }, { "date": "2026-03-29T00:39:33.763771Z", "number": "10", "summary": "Source connected.| CVE status created. (valid)| EPSS created." }, { "date": "2026-03-30T12:41:41.436967Z", "number": "11", "summary": "Unknown change." }, { "date": "2026-04-03T17:25:28.876438Z", "number": "12", "summary": "CVSS created.| Products connected (2).| Product Identifiers created (4).| Products created (2).| Exploits created (1)." }, { "date": "2026-04-03T17:25:38.813185Z", "number": "13", "summary": "NCSC Score updated." } ], "status": "interim", "version": "13" } }, "product_tree": { "branches": [ { "branches": [ { "branches": [ { "category": "product_version_range", "name": "vers:rpm/3", "product": { "name": "vers:rpm/3", "product_id": "CSAFPID-1441150", "product_identification_helper": { "cpe": "cpe:/a:redhat:openshift_devspaces:3:" } } } ], "category": "product_name", "name": "Red Hat OpenShift Dev Spaces" }, { "branches": [ { "branches": [ { "category": "product_version_range", "name": "vers:rpm/unknown", "product": { "name": "vers:rpm/unknown", "product_id": "CSAFPID-2485335" } } ], "category": "product_name", "name": "traefik-rhel9" } ], "category": "product_family", "name": "Red Hat OpenShift Dev Spaces" } ], "category": "vendor", "name": "Red Hat" }, { "branches": [ { "branches": [ { "category": "product_version_range", "name": "vers:unknown/3.7.0-ea1", "product": { "name": "vers:unknown/3.7.0-ea1", "product_id": "CSAFPID-5902893", "product_identification_helper": { "cpe": "cpe:2.3:a:traefik:traefik:3.7.0:ea1:*:*:*:*:*:*" } } }, { "category": "product_version_range", "name": "vers:unknown/3.7.0-ea2", "product": { "name": "vers:unknown/3.7.0-ea2", "product_id": "CSAFPID-5992578", "product_identification_helper": { "cpe": "cpe:2.3:a:traefik:traefik:3.7.0:ea2:*:*:*:*:*:*" } } }, { "category": "product_version_range", "name": "vers:unknown/<2.11.42", "product": { "name": "vers:unknown/<2.11.42", "product_id": "CSAFPID-5941625", "product_identification_helper": { "cpe": "cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*" } } }, { "category": "product_version_range", "name": "vers:unknown/>=3.0.0-beta1|<3.6.11", "product": { "name": "vers:unknown/>=3.0.0-beta1|<3.6.11", "product_id": "CSAFPID-5874589" } }, { "category": "product_version_range", "name": "vers:unknown/>=3.0.0|<3.6.12", "product": { "name": "vers:unknown/>=3.0.0|<3.6.12", "product_id": "CSAFPID-5992577", "product_identification_helper": { "cpe": "cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*" } } }, { "category": "product_version_range", "name": "vers:unknown/>=3.7.0-ea.1|<3.7.0-ea.3", "product": { "name": "vers:unknown/>=3.7.0-ea.1|<3.7.0-ea.3", "product_id": "CSAFPID-5941626" } } ], "category": "product_name", "name": "Traefik" } ], "category": "vendor", "name": "Traefik" } ] }, "vulnerabilities": [ { "cve": "CVE-2026-33433", "cwe": { "id": "CWE-290", "name": "Authentication Bypass by Spoofing" }, "notes": [ { "category": "description", "text": "Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.42, 3.6.11, and 3.7.0-ea.3, when `headerField` is configured with a non-canonical HTTP header name (e.g., `x-auth-user` instead of `X-Auth-User`), an authenticated attacker can inject their own canonical version of that header to impersonate any identity to the backend. The backend receives two header entries — the attacker-injected canonical one is read first, overriding Traefik's non-canonical write. Versions 2.11.42, 3.6.11, and 3.7.0-ea.3 patch the issue.", "title": "cveprojectv5 - https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/33xxx/CVE-2026-33433.json" }, { "category": "description", "text": "Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.42, 3.6.11, and 3.7.0-ea.3, when `headerField` is configured with a non-canonical HTTP header name (e.g., `x-auth-user` instead of `X-Auth-User`), an authenticated attacker can inject their own canonical version of that header to impersonate any identity to the backend. The backend receives two header entries — the attacker-injected canonical one is read first, overriding Traefik's non-canonical write. Versions 2.11.42, 3.6.11, and 3.7.0-ea.3 patch the issue.", "title": "nvd - https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-33433" }, { "category": "description", "text": "## Summary\n\nThere is a potential vulnerability in Traefik's Basic and Digest authentication middlewares when `headerField` is configured with a non-canonical HTTP header name.\n\nAn authenticated attacker with valid credentials can inject the canonical version of the configured header to impersonate any identity to the backend. Because Traefik writes the authenticated username using a non-canonical map key, it creates a separate header entry rather than overwriting the attacker's canonical one — causing most backend frameworks to read the attacker-controlled value instead.\n\n## Patches\n\n- \n- \n- \n\n## For more information\n\nIf there are any questions or comments about this advisory, please [open an issue](https://github.com/traefik/traefik/issues).\n\n---\n\n
\nOriginal Description\n\n### Summary\n\nWhen `headerField` is configured with a non-canonical HTTP header name (e.g., `x-auth-user` instead of `X-Auth-User`), an authenticated attacker can inject a canonical version of that header to impersonate any identity to the backend. The backend receives two header entries — the attacker-injected canonical one is read first, overriding Traefik's non-canonical write.\n\nTested on Traefik v3.6.10.\n\n### Details\n\nAt `pkg/middlewares/auth/basic_auth.go:92`, the authenticated username is written using direct map assignment:\n\n```go\nreq.Header[b.headerField] = []string{user}\n```\n\nGo's `http.Header` map is keyed by canonical names (e.g., `X-Auth-User`). Direct assignment with a non-canonical key (`x-auth-user`) creates a separate map entry from any canonical-key entry already present. The attacker's `X-Auth-User: superadmin` occupies the canonical slot and is never overwritten by Traefik's non-canonical write.\n\nThe same bug exists in `pkg/middlewares/auth/digest_auth.go:100`. Notably, `forward.go:254` correctly uses `http.CanonicalHeaderKey()`, showing the fix pattern already exists in the codebase.\n\n### PoC\n\n**Traefik config (YAML, Docker labels, or REST API):**\n\n```yaml\nmiddlewares:\n auth:\n basicAuth:\n users: [\"admin:$2y$05$...\"]\n headerField: \"x-auth-user\"\n```\n\n**Normal request (baseline):**\n\n```bash\ncurl -u admin:admin http://traefik/secure/test\n# Backend receives: x-auth-user: admin\n# Identity = admin ✓\n```\n\n**Attack request:**\n\n```bash\ncurl -u admin:admin -H \"X-Auth-User: superadmin\" http://traefik/secure/test\n# Backend receives BOTH headers:\n# X-Auth-User: superadmin ← attacker-injected (canonical key, read first by most frameworks)\n# x-auth-user: admin ← Traefik-set (non-canonical, ignored by most frameworks)\n# Identity seen by backend = superadmin ✗\n```\n\n**Control test** — when `headerField` uses canonical casing (`X-Auth-User`), the attack fails. Traefik's write correctly overwrites the attacker's header.\n\nThis is realistic because YAML conventions favor lowercase keys, Traefik docs don't warn about canonicalization, and the pattern of backends trusting the `headerField` header is recommended in Traefik's own documentation.\n\n**Fix suggestion:**\n\n```go\n// basic_auth.go:92 and digest_auth.go:100 — change:\nreq.Header[b.headerField] = []string{user}\n// to:\nreq.Header.Set(b.headerField, user)\n```\n\nAlso strip any incoming `headerField` header before the auth check with `req.Header.Del(b.headerField)`.\n\n### Impact\n\nAn authenticated attacker with valid credentials (even low-privilege) can impersonate any other user identity to backend services. If backends use the `headerField` header for authorization decisions (which is the intended use case per Traefik docs), this enables privilege escalation — e.g., a regular user impersonating an admin.\n\nThe attack requires the operator to configure `headerField` with a non-canonical header name, which is the natural thing to do in YAML and is not warned against in documentation.\n\n
", "title": "github - https://api.github.com/advisories/GHSA-qr99-7898-vr7c" }, { "category": "description", "text": "A flaw was found in Traefik, an HTTP reverse proxy and load balancer. When the `headerField` is configured with a non-canonical HTTP header name, an authenticated attacker can inject a canonical version of that header. This allows the attacker to impersonate any identity to the backend, leading to an authentication bypass. The backend prioritizes the attacker-injected header, overriding Traefik's intended header.", "title": "redhat - https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2026-33433.json" }, { "category": "other", "text": "0.00011", "title": "EPSS" }, { "category": "other", "text": "CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N", "title": "CVSSV4" }, { "category": "other", "text": "5.1", "title": "CVSSV4 base score" }, { "category": "other", "text": "4.1", "title": "NCSC Score" }, { "category": "other", "text": "There is product data available from source Redhat", "title": "NCSC Score top increasing factors" }, { "category": "other", "text": "There is exploit data available from source Nvd", "title": "NCSC Score top decreasing factors" }, { "category": "details", "text": "Severity: 3\n", "title": "Vendor assessment" } ], "product_status": { "known_affected": [ "CSAFPID-5874589", "CSAFPID-5941625", "CSAFPID-5941626", "CSAFPID-1441150", "CSAFPID-2485335", "CSAFPID-5902893", "CSAFPID-5992577", "CSAFPID-5992578" ] }, "references": [ { "category": "external", "summary": "Source - cveprojectv5", "url": "https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/33xxx/CVE-2026-33433.json" }, { "category": "external", "summary": "Source - nvd", "url": "https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-33433" }, { "category": "external", "summary": "Source - github", "url": "https://api.github.com/advisories/GHSA-qr99-7898-vr7c" }, { "category": "external", "summary": "Source - redhat", "url": "https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2026-33433.json" }, { "category": "external", "summary": "Source - first", "url": "https://api.first.org/data/v1/epss?limit=10000&offset=0" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd; redhat", "url": "https://github.com/traefik/traefik/security/advisories/GHSA-qr99-7898-vr7c" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd; redhat", "url": "https://github.com/traefik/traefik/releases/tag/v2.11.42" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd; redhat", "url": "https://github.com/traefik/traefik/releases/tag/v3.6.11" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd; redhat", "url": "https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.3" }, { "category": "external", "summary": "Reference - github; redhat", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-33433" }, { "category": "external", "summary": "Reference - github", "url": "https://github.com/advisories/GHSA-qr99-7898-vr7c" }, { "category": "external", "summary": "Reference - redhat", "url": "https://www.cve.org/CVERecord?id=CVE-2026-33433" } ], "remediations": [ { "category": "mitigation", "details": "Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.", "product_ids": [ "CSAFPID-1441150", "CSAFPID-2485335" ] } ], "scores": [ { "cvss_v3": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 8.8, "baseSeverity": "HIGH" }, "products": [ "CSAFPID-1441150", "CSAFPID-2485335", "CSAFPID-5874589", "CSAFPID-5902893", "CSAFPID-5941625", "CSAFPID-5941626", "CSAFPID-5992577", "CSAFPID-5992578" ] } ], "title": "CVE-2026-33433" } ] }