On the Utilized Programs Group within the SEI’s CERT Division, considered one of our areas of labor focuses on Docker container photos that require hardening to take away vulnerabilities. By way of our work, we’ve seen stakeholders encountering issue with hardening open-source container photos, along with growing routine processes for vulnerability mitigation for Docker container photos.
Utilizing unvetted container photos can enhance safety dangers via the introduction of susceptible software program into a corporation’s software program provide chain. For instance, unvetted container photos may comprise packages with identified Widespread Vulnerabilities and Exposures (CVEs), introducing a possible exploitation vector. As this weblog publish particulars, hardening these container photos, or choosing verified pre-hardened container photos earlier than utilization, decreases the chance of introducing susceptible software program.
Hardening containers and container photos entails analyzing their present safety standing after which making use of remediations to iteratively enhance safety. The hardening course of is routine and offers iterative safety monitoring through the improvement course of. A hardened picture offers a safe sandbox for improvement and execution of open-source software program.
The Container Hardening Course of
Determine 1: The iterative container hardening course of for vulnerability detection and remediation.
The method of hardening containers and container photos begins with a baseline safety scan of the unhardened picture to create a listing of identified vulnerabilities. As soon as this baseline has been made, engineers ought to analyze the picture Dockerfile and substitute any non-standard base photos with respected base photos from verified publishers. Following the rebasing, engineers, utilizing container picture options reminiscent of Docker, ought to start the iterative course of to remediate identified bugs whereas scanning for brand spanking new vulnerabilities.
It is advisable to exchange non-standard photos utilized in a Dockerfile as a result of, as we talked about earlier, photos can deliver vulnerabilities that may discover their method into the top product. This will take the type of susceptible packages or different dependencies utilized by the picture, however it might probably additionally come because of unsecure practices within the picture itself. To counteract this, rebasing the Dockerfile to make use of photos from Docker verified publishers reminiscent of Crimson Hat permits for extra stability in updates and vulnerability mitigation.
These techniques of scanning and substituting photos is actually the beginnings of a software program invoice of supplies (SBOM), and this makes it simpler to create and monitor an SBOM. The outputs of every safety scan assist establish the place actions are wanted when new vulnerabilities come to gentle and might be added to the SBOM to take care of its accuracy.
Decreasing Potential Vulnerabilities in Container Pictures
A number of different practices can be employed when rebasing a Dockerfile to additional mitigate dangers and vulnerabilities. For starters, if a Dockerfile doesn’t make use of it already, engineers can implement a multi-stage construct course of. This enables the construct course of to put in the dependencies wanted to construct parts of the service, whereas leaving these construct dependencies behind of their respective levels. Doing this permits the construct course of to deliver solely what’s required for the ultimate picture into the ultimate construct stage. Leaving these runtime-irrelevant dependencies out of the ultimate picture can scale back the picture’s menace floor.
In the identical vein, a extra minimal base picture can be useful. Constructing a container to serve a database, for instance, is unlikely to wish many of the options of a full working system (OS) base picture. A number of widespread base photos reminiscent of Crimson Hat Common Base Picture(UBI), Debian, and Rocky Linux supply stripped-down variations leaving fewer superfluous and doubtlessly susceptible packages and configurations, and likewise offers the additional advantage of lowering the scale of the ultimate picture. For extra on the subject of lowering the scale of photos, take a look at this SEI presentation by Kevin Pitstick.
There are a number of different tweaks that may additionally assist in lowering potential vulnerabilities in container photos. One in every of these is to substitute using the ADD instruction with the COPY instruction wherever attainable. ADD and COPY overlap in that they will each be used to maneuver native information round through the picture constructing course of. Nevertheless, ADD has the extra functionality of having the ability to obtain information referenced by exterior URLs, in addition to unpackage archives. These extra capabilities might be undesirable additions when safety is a priority. Containers must also be set to run as a non-root service person when attainable, to restrict their means to carry out malicious duties if compromised. Observe that by default, Docker containers run as root. By working a container as a non-root service, the precept of least privilege is adopted. It’s additionally an excellent observe to outline the service person early on in a Dockerfile, switching again to root solely as wanted within the construct course of.
The Significance of Vulnerability Scanning
Vulnerability scanning is a vital step in figuring out vulnerabilities in a container picture. Utilizing instruments reminiscent of Grype and Trivy, safety and infrastructure engineers can routinely run safety scans on open-source photos along with photos constructed through an automatic pipeline. Creating an automatic course of to routinely scan the container picture is a standard a part of most DevSecOps pipelines and can add larger visibility into vulnerability detection. Routine scanning additionally permits for the institution of a vulnerability baseline and incremental mitigation.
Vulnerability scans sometimes yield a listing of CVEs, which comprise details about the vulnerability and any potential mitigations. A CVE normally has a Widespread Vulnerability Scoring System (CVSS) rating, which assesses the severity of the vulnerability. Calculating or wanting up the CVSS rating can streamline the method of prioritizing the remediation of vulnerabilities.
Hardening of Docker photos entails inspection of how the picture is constructed, routinely scanning the constructed picture for vulnerabilities, after which making use of mitigations to the picture constructing course of. The continual technique of scanning new revealed photos helps detect any new vulnerabilities. By establishing a routine course of for hardening photos, confidence is gained within the manufacturing pipeline ranging from the event stage.
