CVE-2026-5545

import pycurl from io import BytesIO # Simulate the vulnerable scenario buffer = BytesIO() c = pycurl.Curl() # Step 1: First request with Negotiate Auth (User1) c.setopt(c.URL, 'https://example.com/resource') c.setopt(c.HTTPAUTH, pycurl.HTTPAUTH_NEGOTIATE) c.setopt(c.USERPWD, 'user1:password1') c.setopt(c.WRITEDATA, buffer) c.perform() print("Request 1 sent with User1 credentials.") # Step 2: Second request with different auth (User2) # In vulnerable versions, this might reuse the connection from Step 1 c.setopt(c.USERPWD, 'user2:password2') c.setopt(c.HTTPAUTH, pycurl.HTTPAUTH_BASIC) # Switch to Basic or other buffer.seek(0) c.setopt(c.WRITEDATA, buffer) c.perform() print("Request 2 sent. If vulnerable, it used User1's connection.") c.close()

{"cve": {"id": "CVE-2026-5545", "sourceIdentifier": "2499f714-1537-4658-8207-48ae4bb9eae9", "published": "2026-05-13T13:01:56.190", "lastModified": "2026-05-13T19:31:07.633", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "libcurl might in some circumstances reuse the wrong connection when asked to\ndo an authenticated HTTP(S) request after a Negotiate-authenticated one, when\nboth use the same host.\n\nlibcurl features a pool of recent connections so that subsequent requests can\nreuse an existing connection to avoid overhead.\n\nWhen reusing a connection a range of criteria must be met. Due to a logical\nerror in the code, a request that was issued by an application could\nwrongfully reuse an existing connection to the same server that was\nauthenticated using different credentials.\n\nAn application that first uses Negotiate authentication to a server with\n`user1:password1` and then does another operation to the same server asking\nfor any authentication method but for `user2:password2` (while the previous\nconnection is still alive) - the second request gets confused and wrongly\nreuses the same connection and sends the new request over that connection\nthinking it uses a mix of user1's and user2's credentials when it is in fact\nstill using the connection authenticated for user1..."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N", "baseScore": 6.5, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "HIGH", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.2, "impactScore": 4.2}, {"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:L/I:H/A:N", "baseScore": 6.5, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "HIGH", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.2, "impactScore": 4.2}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-613"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:haxx:curl:*:*:*:*:*:*:*:*", "versionStartIncluding": "7.10.6", "versionEndExcluding": "8.20.0", "matchCriteriaId": "6863ED61-1229-415E-BB05-C827893B6CED"}]}]}], "references": [{"url": "https://curl.se/docs/CVE-2026-5545.html", "source": "2499f714-1537-4658-8207-48ae4bb9eae9", "tags": ["Patch", "Vendor Advisory"]}, {"url": "https://curl.se/docs/CVE-2026-5545.json", "source": "2499f714-1537-4658-8207-48ae4bb9eae9", "tags": ["Vendor Advisory"]}, {"url": "https://hackerone.com/reports/3642555", "source": "2499f714-1537-4658-8207-48ae4bb9eae9", "tags": ["Exploit", "Issue Tracking", "Third Party Advisory"]}, {"url": "https://hackerone.com/reports/3642555", "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "tags": ["Exploit", "Issue Tracking", "Third Party Advisory"]}]}}