On the Utilized Programs Group within the SEI’s CERT Division, certainly one of our areas of labor focuses on Docker container photos that require hardening to take away vulnerabilities. By our work, we’ve seen stakeholders encountering problem with hardening open-source container photos, along with growing routine processes for vulnerability mitigation for Docker container photos.
Utilizing unvetted container photos can improve safety dangers by the introduction of weak software program into a corporation’s software program provide chain. For instance, unvetted container photos may include packages with recognized Widespread Vulnerabilities and Exposures (CVEs), introducing a possible exploitation vector. As this weblog publish particulars, hardening these container photos, or deciding on verified pre-hardened container photos earlier than utilization, decreases the danger of introducing weak 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 gives iterative safety monitoring in the course of the growth course of. A hardened picture gives a safe sandbox for growth 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 an inventory of recognized vulnerabilities. As soon as this baseline has been made, engineers ought to analyze the picture Dockerfile and exchange any non-standard base photos with respected base photos from verified publishers. Following the rebasing, engineers, utilizing container picture options corresponding to Docker, ought to start the iterative course of to remediate recognized bugs whereas scanning for brand 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 carry vulnerabilities that may discover their manner into the tip product. This may take the type of weak packages or different dependencies utilized by the picture, however it may 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 corresponding to Crimson Hat permits for extra stability in updates and vulnerability mitigation.
These techniques of scanning and substituting photos is basically 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 determine the place actions are wanted when new vulnerabilities come to gentle and will be added to the SBOM to take care of its accuracy.
Decreasing Potential Vulnerabilities in Container Photographs
A number of different practices may also 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 permits 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 enables the construct course of to carry 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 risk floor.
In the identical vein, a extra minimal base picture may also be helpful. Constructing a container to serve a database, for instance, is unlikely to want many of the options of a full working system (OS) base picture. A number of widespread base photos corresponding to Crimson Hat Common Base Picture(UBI), Debian, and Rocky Linux provide stripped-down variations leaving fewer superfluous and probably weak packages and configurations, and in addition provides the additional advantage of decreasing the scale of the ultimate picture. For extra on the subject of decreasing the scale of photos, take a look at this SEI presentation by Kevin Pitstick.
There are just a few different tweaks that may additionally support in decreasing potential vulnerabilities in container photos. Certainly one of these is to exchange the usage of the ADD instruction with the COPY instruction wherever attainable. ADD and COPY overlap in that they’ll each be used to maneuver native recordsdata round in the course of the picture constructing course of. Nevertheless, ADD has the extra functionality of with the ability to obtain recordsdata referenced by exterior URLs, in addition to unpackage archives. These extra capabilities will be undesirable additions when safety is a priority. Containers must also be set to run as a non-root service consumer when attainable, to restrict their skill to carry out malicious duties if compromised. Observe that by default, Docker containers run as root. By operating a container as a non-root service, the precept of least privilege is adopted. It’s additionally follow to outline the service consumer 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 crucial step in figuring out vulnerabilities in a container picture. Utilizing instruments corresponding to Grype and Trivy, safety and infrastructure engineers can routinely run safety scans on open-source photos along with photos constructed by way of an automatic pipeline. Creating an automatic course of to routinely scan the container picture is a typical a part of most DevSecOps pipelines and can add higher visibility into vulnerability detection. Routine scanning additionally permits for the institution of a vulnerability baseline and incremental mitigation.
Vulnerability scans usually yield an inventory of CVEs, which include 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 trying 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 strategy of scanning new printed 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.