Google Online Security Blog: SBOM in Action: finding vulnerabilities with a Software Bill of Materials

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SBOM in Action: finding vulnerabilities with a Software Bill of Materials

June 14, 2022

Posted by Brandon Lum and Oliver Chang, Google Open Source Security Team

SBOMs2021 Executive Order on CybersecuritySecure Software Development Frameworkmaking progress on methodscriticalOSV: Connecting SBOMs to vulnerabilitiesbomOpen Source Vulnerabilities (OSV) databaseGithub Advisory Database (GHSA)Global Security Database (GSD)spdx-to-osvpublicly available

# Download the Kubernetes SPDX source document

$ curl -L https://sbom.k8s.io/v1.21.3/source > k8s-1.21.3-source.spdx

spdx-to-osv

# Run the spdx-to-osv tool, taking the information from the SPDX SBOM and mapping it to OSV vulnerabilities

$ java -jar ./target/spdx-to-osv-0.0.4-SNAPSHOT-jar-with-dependencies.jar -I k8s-1.21.3-source.spdx -O out-k8s.1.21.3.json

# Show the output OSV vulnerabilities of the spdx-to-osv tool

$ cat out-k8s.1.21.3.json

…

{

"id": "GHSA-w73w-5m7g-f7qc",

"published": "2021-05-18T21:08:21Z",

"modified": "2021-06-28T21:32:34Z",

"aliases": [

"CVE-2020-26160"

"summary": "Authorization bypass in github.com/dgrijalva/jwt-go",

"details": "jwt-go allows attackers to bypass intended access restrictions in situations with []string{} for m[\"aud\"] (which is allowed by the specification). Because the type assertion fails, \"\" is the value of aud. This is a security problem if the JWT token is presented to a service that lacks its own audience check. There is no patch available and users of jwt-go are advised to migrate to [golang-jwt](https://github.com/golang-jwt/jwt) at version 3.2.1",

"affected": [

{

"package": {

"name": "github.com/dgrijalva/jwt-go",

"ecosystem": "Go",

"purl": "pkg:golang/github.com/dgrijalva/jwt-go"

…

CVE-2020-26160
Suggestions for SBOM tooling improvements

To get the spdx-to-osv tool to work we had to make some minor changes to disambiguate the information provided in the SBOM:

In the current implementation of the bom tool, the version was included as part of the package name (gopkg.in/square/go-jose.v2@v2.2.2). We needed to trim the suffix to match the SPDX format, which has a different field for version number.

The SBOM created by the bom tool does not specify an ecosystem. Without an ecosystem, it's impossible to reliably disambiguate which library or package is affected in an automated way. Vulnerability scanners could return false positives if one ecosystem was affected but not others. It would be more helpful if the SBOM differentiated between different library and package versions.

These are relatively minor hurdles, though, and we were able to successfully run the tool with only small manual adjustments. To make the process easier in the future, we have the following recommendation for improving SBOM generation tooling:

SBOM tooling creators should add a reference using an identification scheme such as Purl for all packages included in the software. This type of identification scheme both specifies the ecosystem and also makes package identification easier, since the scheme is more resilient to small deviations in package descriptors like the suffix example above. SPDX supports this via external references to Purl and other package identification schemas.

SBOM in the future

It’s clear that we’re getting very close to achieving the original goal of SBOMs: using them to help manage the risk of vulnerabilities in software. Our example queried the OSV database, but we will soon see the same success in mapping SBOM data to other vulnerability databases and even using them with new standards like VEX, which provides additional context around whether vulnerabilities in software have been mitigated.

Continuing on this path of widespread SBOM adoption and tooling refinement, we will hopefully soon be able to not only request and download SBOMs for every piece of software, but also use them to understand the vulnerabilities affecting any software we consume. This example is a peek into a possible future of what SBOMs can offer when we bridge the gap to connect them with vulnerability databases: a new normal of worrying less about the risks in the software we use.