On the Utilized Methods Group within the SEI’s CERT Division, one among our areas of labor focuses on Docker container photographs that require hardening to take away vulnerabilities. By means of our work, we’ve seen stakeholders encountering issue with hardening open supply container photographs, along with growing routine processes for vulnerability mitigation for Docker container photographs.
Utilizing unvetted container photographs can enhance safety dangers by the introduction of susceptible software program into a company’s software program provide chain. For instance, unvetted container photographs might comprise packages with recognized Widespread Vulnerabilities and Exposures (CVEs), introducing a possible exploitation vector. As this weblog publish particulars, hardening these container photographs, or choosing verified pre-hardened container photographs earlier than utilization, decreases the danger of introducing susceptible software program.
Hardening containers and container photographs 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 photographs begins with analyzing the picture Dockerfile and changing any non-standard base photographs with respected base photographs from verified publishers. As soon as this variation has been made, a baseline safety scan of the unhardened picture ought to be created to determine a listing 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 interchange non-standard photographs utilized in a Dockerfile as a result of, as we talked about earlier, photographs can carry vulnerabilities that may discover their manner into the top product. This may take the type of susceptible packages or different dependencies utilized by the picture, however it may well additionally come on account of unsecure practices within the picture itself. To counteract this, rebasing the Dockerfile to make use of photographs from Docker verified publishers comparable to Pink Hat permits for extra stability in updates and vulnerability mitigation.
These ways of scanning and substituting photographs 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 establish the place actions are wanted when new vulnerabilities come to gentle and could be added to the SBOM to keep up 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 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 can 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 photographs comparable to Pink Hat Common Base Picture (UBI), Debian, and Rocky Linux supply stripped-down variations leaving fewer superfluous and doubtlessly susceptible packages and configurations, and in addition provides the additional advantage of lowering the scale of the ultimate picture.
There are a number of different tweaks that may additionally help in lowering potential vulnerabilities in container photographs. One among 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. Nonetheless, ADD has the extra functionality of having the ability to obtain recordsdata referenced by exterior URLs, in addition to unpackage archives. These extra 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. Be aware 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 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 vital 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 photographs along with photographs 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 better 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 often 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 photographs 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 printed photographs helps detect any new vulnerabilities. By establishing a routine course of for hardening photographs, confidence is gained within the manufacturing pipeline ranging from the event stage.