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Anthropic’s OSS Scanner is a free, opt-in security scanning service for open-source projects. A lead maintainer or an authorized delegate enrolls by opening a pull request in Anthropic’s oss-scanner repository with a projects/<project>/project.yaml file and a buildable Dockerfile. Anthropic reviews eligibility and maintainer authority case by case.
The strongest candidates are established projects whose defects could affect infrastructure or user security, especially code that processes untrusted input and has many users or dependent projects. Enrollment also requires a reliable offline-audit build and enough maintainer capacity to investigate model-generated reports, including false positives and incorrect severity ratings.
What Anthropic’s OSS Scanner does
OSS Scanner analyzes enrolled open-source projects for security vulnerabilities and other bugs. The service is free, but it is not an automatic public sign-up. Anthropic chooses projects individually and can change its criteria as the enrollment pipeline changes.
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The first accepted scan produces a bundle of reports delivered by email. Later scans are intended to identify vulnerabilities introduced since the previous scan and issues earlier scans missed. Anthropic does not promise a fixed interval: frequency depends on pipeline capacity and usage.
Check whether your project is likely to qualify
Eligibility is not determined by a published score or minimum download count. Anthropic describes the process as case by case and points to criteria similar to Google’s OSS-Fuzz program: “We accept established projects that have a critical impact on infrastructure and user security.” Use the checks below to prepare an honest explanation, not as a guarantee of acceptance.
| Question | What supports a strong case | What to document |
|---|---|---|
| Is the project established and security-important? | It is widely used in infrastructure, production systems, or security-sensitive software, and a defect could harm users or other services. | Public adoption evidence, deployment context, and a short explanation of the security impact if it is not obvious from the project homepage. |
| Can an attacker reach the relevant code? | The project parses network traffic, files, requests, protocols, packages, or other untrusted input. Anthropic’s FAQ specifically identifies remote-attack exposure as a consideration. | Entry points, trust boundaries, and examples of how untrusted data reaches the code. |
| How broad is the downstream reach? | Many users, distributions, services, or dependent projects rely on the library or application. | Approximate user and dependent-project counts, with the source or method used to estimate them. |
| Can maintainers handle findings? | The team can reproduce, assess, prioritize, and fix verified high- and critical-severity issues, while also reviewing questionable findings. | Named security contacts, response ownership, and a practical process for triage and coordinated fixes. |
| Can the project build for an offline audit? | A Dockerfile installs every dependency and builds or tests the project before the scanner loses network access. | The Dockerfile path, required build arguments, test command, supported platforms, and any non-network assets needed at runtime. |
If the project’s importance is not self-evident, include a concise explanation in the project’s public documentation or enrollment context. Anthropic may decline a submission that otherwise resembles an eligible project, and it may revise the criteria later.
Confirm who is allowed to enroll
The person opening the pull request must be the project’s lead maintainer or must have that maintainer’s authorization. If an employee maintains a project on behalf of an organization that is the lead maintainer, obtain the organization’s permission as well. Anthropic may contact project leadership through another channel before accepting the enrollment.
Choose a primary contact who monitors security mail. You can list additional recipients with the optional auto_ccs field and can provide a PGP key with pgp when encrypted delivery is appropriate. Only authorized project maintainers may use the reports, and Anthropic’s terms restrict their use to identifying, assessing, and fixing vulnerabilities and other bugs in the project.
Prepare the repository and build
Make the build deterministic
The Dockerfile referenced by the configuration must install dependencies and build the project. Anthropic builds it with internet access, then runs the security audit offline. Pin or otherwise control dependency resolution where practical, copy required source and test fixtures into the image, and ensure the build does not depend on a service that will disappear when networking is disabled.
Decide what the scanner should understand
An optional threat model can describe project-specific trust boundaries, risky components, or scanner preferences that are not documented elsewhere. Unless you specify another location, Anthropic looks for .oss-scanner/threat_model.md. Keep the document focused on facts that change how a finding should be interpreted.
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The required fields are:
repo: the Git repository URL, optionally followed by#branch.primary_contact: the main email address for reports.Dockerfile: a repository-relative path to the Dockerfile that installs dependencies and builds the project.
The repository itself does not have to be hosted on GitHub. If you place a file named Dockerfile beside project.yaml in Anthropic’s repository, you can omit the Dockerfile field.
Enroll through a pull request
- Verify authority and contacts. Confirm lead-maintainer or organizational approval, select a monitored primary email address, and decide whether additional recipients or PGP encryption are needed.
- Open the template repository. Fork or otherwise create a working branch from Anthropic’s oss-scanner repository. Add a directory named
projects/<project>/and createproject.yamlinside it. - Add the required configuration. A minimal illustrative file looks like this:
repo: 'https://git-host.example/org/project#main'
primary_contact: 'security@project.example'
Dockerfile: 'build/Dockerfile'The host and addresses above are examples; replace them with the project’s real values. The branch suffix is optional. Use a repository-relative Dockerfile path, not a path on your workstation.
- Add optional context. The FAQ lists
auto_ccs,homepage,threat_model,pgp, anddisabled. For example, a fuller configuration can identify a project homepage, point to a non-default threat-model file, or setdisabled: truewhen pausing an enrolled project. Include only fields that are useful and valid for your project. - Validate before submitting. From a checkout of the scanner repository, run Anthropic’s validation script,
tools/validate.py. Then build the configured Dockerfile locally with the same context and arguments the enrollment will use. Run the project’s test cases inside the resulting container and fix failures before opening the pull request. - Open the pull request. Submit the change adding
projects/<project>/project.yaml. Explain any unusual build requirement or eligibility rationale in the pull request description so reviewers can understand the submission.
What Anthropic checks after submission
Anthropic manually verifies that the submitter is a core maintainer or otherwise authorized. It then attempts the container build on its infrastructure. Anthropic says it will email promptly if the build fails so maintainers can correct the configuration or Dockerfile.
Acceptance remains discretionary. A project can meet several indicators and still be declined, and Anthropic may adjust the criteria as more projects enter the pipeline. Do not treat an open pull request as enrollment; scanning begins only after acceptance and a successful build.
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Understand the reports before opting in
Reports are leads, not confirmed defects
OSS Scanner reports are model-generated without human review or triage. Anthropic warns that a report can be invalid, incomplete, or assigned an inflated severity. A suggested patch may be incomplete or may break existing functionality. For every report, reproduce the behavior, inspect the affected code and data flow, determine practical exploitability, and test any fix in the project’s own environment.
How strong were the early results?
In a 2026 expert penetration-tester review, Anthropic said 85 of 97 critical- and high-severity findings across 48 projects met the testers’ coordinated-vulnerability-disclosure bar, an 88% proportion within that evaluation. Of the other 12 findings, Anthropic said 11 were real but duplicates of known issues or other findings from the same scan, while one was invalid. This is a bounded evaluation statistic, not a guaranteed accuracy rate for future scans.
Anthropic’s October 8, 2026 launch post also reported that the separate CyberGym academic benchmark rose from finding under 20% of vulnerabilities at the beginning of the prior year to more than 85% that year. CyberGym is a different benchmark and should not be interpreted as an OSS Scanner result.
What maintainers reported
PostgreSQL contributor Noah Misch said during early validation: “An unusually high fraction of OSS Scanner’s findings uncovered PostgreSQL defects. Several reports came with fixes we can use nearly as-is, and fast-track access let us address the newest issues before they reached a GA release.” That is one maintainer’s experience during validation, not a promise about every project or report.
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Confidentiality, storage, and disclosure
Anthropic says reports are stored in an isolated, locked-down cloud project accessible only to security staff who need access. Scanning agents run in hardened sandboxes after internet access is disabled. Reports are confidential, supplied “as is,” and may be shared with authorized project maintainers for vulnerability and bug remediation.
Unvalidated OSS Scanner findings do not receive a 90-day coordinated-disclosure period. If Anthropic later validates a report manually through its CVD program, it may disclose under that policy beginning 90 days after notifying the maintainer of human validation. Anthropic has said it may consider disclosure periods for some high-severity reports in the future; if that approach changes, it says maintainers will receive notice and an opt-out option.
Pause scanning or leave the program
Pause reports temporarily
Submit a pull request that sets disabled: true in the project configuration. Use this when the team needs to stop incoming reports without deleting the enrollment record. Coordinate the change with the project’s security contacts so the state is understood.
Opt out completely
Submit a pull request removing the project’s entire projects/<project>/ directory. After opting out, the project returns to receiving reports only through Anthropic’s standard CVD process, rather than OSS Scanner’s enrollment pipeline.
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Decide whether the operational cost is acceptable
| Decision area | Ready to enroll when… | Delay or improve when… |
|---|---|---|
| Security impact | The project’s infrastructure or user-security importance and remote attack surface are clear. | The project’s impact is difficult to explain or the relevant code is not exposed to untrusted input. |
| Maintainer capacity | A named team can reproduce findings, challenge incorrect severity, and fix verified high- and critical-severity issues. | There is no reliable security owner or the team cannot process confidential reports promptly. |
| Build readiness | The Dockerfile succeeds locally, tests pass in the container, and all audit-time inputs are available offline. | The build downloads dependencies during tests, requires unavailable services, or fails intermittently. |
| Information handling | Contacts understand the confidentiality and permitted-use terms, and email or PGP handling is dependable. | Reports would go to an unmonitored address or cannot be restricted to authorized maintainers. |
| Reversibility | The project is prepared to pause with disabled: true or remove its directory if the workload becomes unsuitable. |
The team has no agreed owner for changing enrollment status. |
Troubleshoot common enrollment problems
The pull request is questioned on eligibility
Explain the project’s infrastructure or user-security role, identify remotely reachable attack paths, and provide approximate user or dependent-project reach. These details address the factors Anthropic’s FAQ names without claiming that any one number guarantees acceptance.
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The configuration is rejected
Check that the directory is exactly projects/<project>/project.yaml, required keys are spelled correctly, the repository URL is valid, and the Dockerfile path is relative to that repository. If the Dockerfile sits beside project.yaml in Anthropic’s repository, remove the Dockerfile key rather than pointing to a nonexistent repository path.
The local build passes but Anthropic’s build fails
Compare the build context, branch, arguments, platform assumptions, and dependency sources. Eliminate hidden access to workstation files or network services. Put every required source file, fixture, and tool installation in the Dockerfile or its build context, then rerun the project’s tests inside the container.
A report appears wrong or too severe
Do not merge a suggested patch solely because the scanner produced it. Reproduce the behavior, check whether the input is attacker-controlled, compare the claimed severity with the project’s threat model, and record why the issue is valid, a duplicate, non-exploitable, or invalid. The service is explicitly intended for maintainers able to perform this assessment.
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Pause the project by setting disabled: true. If the pause will be permanent, remove the project directory through a pull request. Agree on a sustainable contact and triage process before requesting re-enrollment.
Practical pre-submission checklist
- A lead maintainer or authorized organizational representative approved enrollment.
- The project’s security importance, remote attack surface, and downstream reach are documented.
primary_contactreaches a monitored mailbox; optional recipients and PGP details are correct.repopoints to the intended repository and branch.- The Dockerfile installs dependencies and builds or tests the project without relying on audit-time internet access.
tools/validate.pypasses, the container build succeeds locally, and tests pass inside it.- The team understands that findings are confidential, model-generated, potentially wrong, and not automatically covered by a 90-day disclosure period.
- Maintainers know how to pause or remove the enrollment configuration.
The Bottom Line
Enroll only if your project has material infrastructure or user-security impact, can be built for an offline audit, and has maintainers ready to investigate imperfect reports. Submit the required project.yaml pull request, expect case-by-case review, and use the configuration pull request to pause or leave whenever the operational burden outweighs the benefit.
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