CVE-2026-33997: 
cAdvisor vulnerability analysis and mitigation

CVE-2026-33997 is an off-by-one error in Moby (Docker Engine)'s plugin privilege validation logic that allows a malicious plugin to bypass the privilege approval flow during docker plugin install. Discovered and reported by Cody (c@wormhole.guru) and disclosed on March 25, 2026, it affects all Moby/Docker Engine versions prior to 29.3.1, as well as github.com/docker/docker Go module versions prior to 29.3.1 and github.com/moby/moby/v2 prior to 2.0.0-beta.8. Docker Desktop is not affected as it does not support plugins. The GitHub Advisory Database assigns a CVSS v3.1 score of 6.8 (Moderate), while Feedly's estimate places it at 8.1 (High) (GitHub Advisory, Moby Advisory).

The root cause is classified as CWE-193 (Off-by-one Error) in the Docker daemon's privilege comparison logic during plugin installation. When a user runs docker plugin install, the daemon computes the privileges required by the plugin's configuration and compares them against the set approved by the user — but due to the off-by-one flaw, this comparison can be bypassed, causing the daemon to accept a privilege set that differs from what was approved. Notably, plugins that request exactly one privilege are also affected because no comparison is performed at all in that case. A fix was committed in moby/moby@f4d6f25 (GitHub Advisory, Moby Advisory).

Successful exploitation allows a malicious plugin to gain elevated permissions beyond what the user intended to approve, potentially including highly sensitive permissions such as broad device access on the host system. This could lead to high confidentiality and integrity impact on the affected Docker host, as unauthorized device access may enable reading sensitive host data or modifying system state. Availability is not directly impacted. The attack surface is limited to environments where Docker plugins are actively installed, and Docker Desktop users are not affected (GitHub Advisory, Moby Advisory).

There is no public proof-of-concept exploit and no confirmed in-the-wild exploitation as of the time of this report (GitHub Advisory). The EPSS score is approximately 0.011–0.019%, indicating a very low near-term exploitation probability. Exploitation requires user interaction — specifically, a user must be socially engineered into installing a plugin from a malicious source — and Docker plugins are relatively uncommon in typical deployments. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. No threat actor attribution has been reported.

1. Craft a malicious plugin: An attacker creates a Docker plugin with a configuration that requests elevated privileges (e.g., broad device access) beyond what would normally be approved, exploiting the off-by-one error in the privilege comparison logic.
2. Host the plugin: The attacker publishes the malicious plugin to a public or attacker-controlled Docker registry to make it installable.
3. Social engineering: The attacker convinces a target user or administrator to install the plugin using docker plugin install <malicious-plugin>, potentially disguising it as a legitimate utility.
4. Privilege bypass triggered: During installation, the Docker daemon's flawed comparison logic fails to correctly validate the plugin's requested privileges against those approved by the user, accepting the elevated privilege set.
5. Gain elevated access: The installed plugin operates with unapproved elevated permissions (e.g., broad device access), which the attacker can leverage to access sensitive host resources or escalate further (GitHub Advisory, Moby Advisory).

• Logs: Docker daemon logs (/var/log/docker.log or journalctl -u docker) showing docker plugin install events for unfamiliar or unrecognized plugin names; privilege approval prompts accepted for plugins with device-access or other sensitive permissions.
• File System: Presence of unexpected plugin directories under /var/lib/docker/plugins/; plugin configuration files (config.json) listing elevated capabilities such as devices or mounts to sensitive host paths.
• Process: Unusual processes spawned by plugin runtimes with elevated host access; plugin containers accessing /dev devices not expected for the plugin's stated purpose.
• Network: Outbound connections from plugin processes to unknown external IPs, potentially indicating data exfiltration following privilege escalation (GitHub Advisory).

Update Moby/Docker Engine to version 29.3.1 or later, which includes the fix for this vulnerability (moby/moby@f4d6f25); users of the moby/moby/v2 Go module should upgrade to 2.0.0-beta.8 or later (Moby Release). If immediate upgrade is not possible, apply the following workarounds: (1) do not install plugins from untrusted sources; (2) carefully review all privileges requested during docker plugin install; (3) restrict Docker daemon access to trusted parties following the principle of least privilege; and (4) avoid relying on plugin privilege approval as the sole security control in sensitive environments (Moby Advisory).

The vulnerability was reported by independent researcher Cody (c@wormhole.guru) and acknowledged by the Moby maintainer vvoland, who published the advisory and patch on March 25, 2026 (Moby Advisory). The fix was bundled with three other security fixes in the Docker Engine 29.3.1 release, suggesting a coordinated security release cycle (Moby Release). Downstream Linux distributions including openSUSE and Amazon Linux 2023 have issued their own security advisories incorporating the fix. No significant social media controversy or broad community debate has been observed, consistent with the moderate severity and limited attack surface of the vulnerability.