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. Via our work, we’ve seen stakeholders encountering problem with hardening open supply container photos, along with creating routine processes for vulnerability mitigation for Docker container photos.
Utilizing unvetted container photos can enhance safety dangers by way of the introduction of susceptible software program into a company’s software program provide chain. For instance, unvetted container photos might include packages with recognized Frequent 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 chance of introducing susceptible software program.
Hardening containers and container photos includes 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 throughout the improvement course of. A hardened picture offers a safe sandbox for improvement and execution of open supply software program.
The Container Hardening Course of
The method of hardening containers and container photos begins with analyzing the picture Dockerfile and changing any non-standard base photos with respected base photos from verified publishers. As soon as this alteration 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, resembling 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 approach into the tip product. This will take the type of susceptible 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 photos from Docker verified publishers resembling Pink 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 will be added to the SBOM to take care of its accuracy.
Lowering Potential Vulnerabilities in Container Photos
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 elements 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 cut 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 frequent base photos resembling Pink Hat Common Base Picture (UBI), Debian, and Rocky Linux supply stripped-down variations leaving fewer superfluous and probably susceptible packages and configurations, and in addition provides the additional benefit of lowering the dimensions of the ultimate picture.
There are a couple of different tweaks that may additionally support in lowering potential vulnerabilities in container photos. One in every of these is to change using the ADD instruction with the COPY instruction wherever potential. 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 having 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 potential, to restrict their skill 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 superb observe 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 resembling Grype and Trivy, safety and infrastructure engineers can routinely run safety scans on open supply photos along with photos constructed by way of 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 usually yield an inventory of CVEs, which include details about the vulnerability and any potential mitigations. A CVE often has a Frequent 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 includes 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 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.
