Incus - CraftedSignal Threat Feed

Critical Incus Vulnerability (CVE-2026-48752) Allows Host Arbitrary File Read/Write Leading to RCE

hello@craftedsignal.io — Fri, 03 Jul 2026 10:37:30 +0000

A critical vulnerability tracked as CVE-2026-48752 has been identified in Incus, a Linux container manager, affecting versions prior to 7.2.0. This flaw allows a malicious actor to perform arbitrary file read and write operations on the underlying host system. The exploitation vector involves crafting a malicious container image or instance backup that includes a top-level templates symlink. When Incus unpacks such an artifact, it fails to properly sanitize this symlink, enabling the attacker to redirect operations intended for the templates directory to any arbitrary path on the host, such as /etc/cron.d. This capability can be leveraged to inject malicious cron jobs or modify other sensitive system files, ultimately leading to arbitrary command execution with root privileges on the host. This vulnerability poses a significant risk to the integrity and security of systems running vulnerable Incus instances.

Attack Chain

The attacker crafts a malicious Incus container image or instance backup (.tar archive).
Within this archive, a top-level symlink named templates is created, pointing to a sensitive host directory (e.g., /etc/cron.d).
The attacker distributes this malicious image or backup, which is then imported or restored on a vulnerable Incus host using incus image import or incus import.
During the unpacking process, Incus's archive.Unpack (for images) or rsync.LocalCopy (for backups) follows the templates symlink due to insufficient sanitization.
The attacker then uses incus config template create or incus config template edit commands, targeting the newly imported malicious instance/image.
Due to the symlink, these incus commands inadvertently write arbitrary content to the sensitive host directory (e.g., creating a new cron job file in /etc/cron.d).
The malicious cron job is executed by the host's cron daemon, achieving arbitrary command execution, often as root, on the host system.
The attacker gains full control over the Incus host, enabling further malicious activities like data exfiltration or deploying additional malware.

Impact

The successful exploitation of CVE-2026-48752 leads to arbitrary file read and write capabilities on the Incus host system. This direct access to the host filesystem allows attackers to modify critical system files, inject malicious configurations (such as cron jobs), and ultimately achieve arbitrary command execution, often with root privileges. The consequences include complete system compromise, unauthorized data access, persistence mechanisms, and potential disruption of services. While no specific victim count or sectors are mentioned, any organization utilizing vulnerable Incus installations could be at risk of severe security breaches and operational disruption.

Recommendation

Patch Incus immediately to version 7.2.0 or newer to address CVE-2026-48752 as advised by the vendor.
Deploy the Sigma rule below to detect suspicious incusd write operations to sensitive system directories.
Enable comprehensive file_event logging for Linux systems to capture modifications within critical directories like /etc/cron.d/, /etc/, /bin/, /sbin/ by the incusd process.

Incus S3 Multipart Upload Path Traversal Leading to RCE (CVE-2026-48753)

hello@craftedsignal.io — Fri, 03 Jul 2026 10:36:22 +0000

A critical path traversal vulnerability, tracked as CVE-2026-48753, has been identified in the Incus incusd daemon affecting versions prior to 7.1.0. This flaw resides within the S3 protocol's multipart upload endpoint, specifically in the handling of the uploadId parameter. Attackers can leverage this unsanitized parameter to inject path traversal sequences (e.g., ../../) and write arbitrary files to sensitive locations on the host system. This arbitrary file write capability can be escalated to achieve persistent arbitrary command execution, for instance, by creating malicious cron jobs in /etc/cron.d. The successful exploitation of this vulnerability would grant an unauthenticated attacker the ability to execute commands with the privileges of the Incus service, posing a significant risk of full system compromise for affected Linux deployments utilizing Incus's S3 functionality.

Attack Chain

Attacker identifies a vulnerable Incus instance (version < 7.1.0) with an exposed S3 API, typically via incus config set core.storage_buckets_address.
The attacker crafts a multipart S3 PUT request, targeting an S3 bucket configured on the vulnerable Incus instance.
The uploadId query parameter within the PUT request is maliciously manipulated, containing path traversal sequences such as ../../../../etc/cron.d.
The request body is populated with the content of a malicious cron job entry, for example, * * * * * root /bin/sh -c 'id > /incus-s3-uploadid-bash-rce; rm -f /etc/cron.d/part-00001'.
Due to the vulnerability in internal/server/storage/s3/local/multipart.go, Incus concatenates the unsanitized uploadId directly into the target file path during the upload process.
This results in an arbitrary file write on the host system, placing the malicious cron job content into a file like /etc/cron.d/part-00001.
The system's cron daemon periodically executes entries found in /etc/cron.d, triggering the newly created malicious job, leading to arbitrary command execution (e.g., id > /incus-s3-uploadid-bash-rce).
The executed cron job also includes a command to delete itself (rm -f /etc/cron.d/part-00001), providing persistent remote code execution while attempting to remove forensic evidence.

Impact

The primary impact of CVE-2026-48753 is the ability for an unauthenticated attacker to achieve arbitrary file write on the host system where Incus is running. This directly enables arbitrary command execution, as demonstrated by the ability to install persistent cron jobs. Successful exploitation can lead to a complete compromise of the Incus host, allowing attackers to establish persistence, exfiltrate data, disrupt services, or pivot to other systems within the network. This vulnerability is critical due to its unauthenticated nature and the severe consequences of command execution.

Recommendation

Patch CVE-2026-48753 immediately by upgrading your Incus installation to version 7.1.0 or later as advised by the advisory.
Deploy the Sigma rule in this brief to your SIEM/EDR to detect exploitation attempts of CVE-2026-48753 by monitoring for suspicious S3 PUT requests.
Monitor web server access logs for HTTP PUT requests to S3 endpoints that contain path traversal sequences (../../ or ..%2F..%2F) in the uploadId query parameter.
Enable comprehensive file integrity monitoring for critical system directories like /etc/cron.d, /tmp, and other common locations for malicious file drops.