On the Utilized Programs Group within the SEI’s CERT Division, considered one of our areas of labor focuses on Docker container pictures that require hardening to take away vulnerabilities. Via our work, we’ve seen stakeholders encountering issue with hardening open supply container pictures, along with creating routine processes for vulnerability mitigation for Docker container pictures.
Utilizing unvetted container pictures can enhance safety dangers by the introduction of weak software program into a corporation’s software program provide chain. For instance, unvetted container pictures might include packages with recognized Widespread Vulnerabilities and Exposures (CVEs), introducing a possible exploitation vector. As this weblog put up particulars, hardening these container pictures, or deciding on verified pre-hardened container pictures earlier than utilization, decreases the chance of introducing weak software program.
Hardening containers and container pictures 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 throughout the improvement course of. A hardened picture gives a safe sandbox for improvement and execution of open supply software program.
The Container Hardening Course of
The method of hardening containers and container pictures begins with analyzing the picture Dockerfile and changing any non-standard base pictures with respected base pictures from verified publishers. As soon as this variation has been made, a baseline safety scan of the unhardened picture must be created to ascertain an inventory of recognized vulnerabilities. Following the creation of a baseline safety scan, engineers utilizing container picture options, akin to Docker, ought to start the iterative course of to remediate recognized bugs whereas scanning for brand new vulnerabilities.
It is advisable to interchange non-standard pictures utilized in a Dockerfile as a result of, as we talked about earlier, pictures can carry vulnerabilities that may discover their manner into the top product. This will take the type of weak packages or different dependencies utilized by the picture, however it may well additionally come because of unsecure practices within the picture itself. To counteract this, rebasing the Dockerfile to make use of pictures from Docker verified publishers akin to Purple Hat permits for extra stability in updates and vulnerability mitigation.
These ways of scanning and substituting pictures 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 could be added to the SBOM to keep up its accuracy.
Lowering Potential Vulnerabilities in Container Photos
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 phases. Doing this permits 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 cut back the picture’s risk floor.
In the identical vein, a extra minimal base picture can be helpful. Constructing a container to serve a database, for instance, is unlikely to want a lot of the options of a full working system (OS) base picture. A number of widespread base pictures akin to Purple Hat Common Base Picture (UBI), Debian, and Rocky Linux supply stripped-down variations leaving fewer superfluous and probably weak packages and configurations, and in addition provides the additional benefit of lowering the scale of the ultimate picture.
There are a number of different tweaks that may additionally support in lowering potential vulnerabilities in container pictures. One in every of these is to exchange using the ADD instruction with the COPY instruction wherever doable. ADD and COPY overlap in that they will each be used to maneuver native recordsdata round throughout 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 further capabilities could be undesirable additions when safety is a priority. Containers also needs to be set to run as a non-root service consumer when doable, to restrict their potential to carry out malicious duties if compromised. Word 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 a very good apply 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 akin to Grype and Trivy, safety and infrastructure engineers can routinely run safety scans on open supply pictures along with pictures 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 better visibility into vulnerability detection. Routine scanning additionally permits for the institution of a vulnerability baseline and incremental mitigation.
Vulnerability scans sometimes 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 pictures 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 pictures helps detect any new vulnerabilities. By establishing a routine course of for hardening pictures, confidence is gained within the manufacturing pipeline ranging from the event stage.