On the Utilized Methods Group within the SEI’s CERT Division, one among 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 growing routine processes for vulnerability mitigation for Docker container photos.
Utilizing unvetted container photos can enhance safety dangers by means of the introduction of weak software program into a company’s software program provide chain. For instance, unvetted container photos might include packages with recognized 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 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 supplies iterative safety monitoring throughout the growth course of. A hardened picture supplies a safe sandbox for growth 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 determine an inventory of recognized vulnerabilities. Following the creation of a baseline safety scan, engineers utilizing container picture options, comparable to Docker, ought to start the iterative course of to remediate recognized 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 carry vulnerabilities that may discover their method into the tip product. This may take the type of weak packages or different dependencies utilized by the picture, however it could possibly additionally come on account of unsecure practices within the picture itself. To counteract this, rebasing the Dockerfile to make use of photos from Docker verified publishers comparable 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 keep up its accuracy.
Lowering Potential Vulnerabilities in Container Pictures
A number of different practices will 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 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 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 will also 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 photos comparable to Crimson 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 offers the additional benefit of lowering the dimensions of the ultimate picture.
There are just a few different tweaks that may additionally help in lowering potential vulnerabilities in container photos. One among these is to change the usage of the ADD instruction with the COPY instruction wherever doable. ADD and COPY overlap in that they’ll each be used to maneuver native information round throughout the picture constructing course of. Nevertheless, ADD has the extra functionality of with the ability to obtain information referenced by exterior URLs, in addition to unpackage archives. These further capabilities will be undesirable additions when safety is a priority. Containers must also be set to run as a non-root service person when doable, to restrict their capability 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 great apply 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 crucial step in figuring out vulnerabilities in a container picture. Utilizing instruments comparable to Grype and Trivy, safety and infrastructure engineers can routinely run safety scans on open supply 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 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 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.