@postalsys/bounce-classifier classifies SMTP bounce messages into actionable categories with a bundled machine learning model that runs locally in Node.js or the browser. The bounce text it classifies comes from remote mail servers and can be attacker-controlled. We welcome responsible reports of vulnerabilities that present a credible security risk to users. Please distinguish security vulnerabilities from ordinary bugs, unusual edge cases, and hardening suggestions.

Security fixes are released only against the latest major version. We do not backport patches to older majors, so upgrading to the current release line is the supported way to receive security updates.

If you are on an older major, please upgrade. See the release notes at https://github.com/postalsys/bounce-classifier/releases before updating.

A security report should identify a realistic way for an attacker to cross a security boundary in a supported version of @postalsys/bounce-classifier. Unexpected behavior, a failing test, or a technically correct proof of concept is not sufficient on its own to establish security impact.

In particular, explain:

• Attacker capabilities: Who is the attacker, and what inputs, systems, or responses can they control without already having the privileges or secrets they are trying to gain?
• Attack path: How does attacker-controlled input reach the affected code through a supported public API or a realistic application integration?
• Prerequisites: What configuration and user actions are required? If the attack depends on unusual options or deliberately malformed input, explain why those conditions could arise in a real application.
• Impact: What confidentiality, integrity, or availability boundary is crossed, and what can the attacker achieve as a result?

A vulnerability involving an optional or less common feature can still qualify if these conditions are met. Conversely, the existence of a defensive check in the code does not, by itself, establish that every bypass of that check has a realistic security impact.

Do not disclose suspected exploitable vulnerabilities through public GitHub issues, pull requests, or discussions before coordinating with the maintainers.

Report privately through one of the following channels:

1. GitHub Security Advisories (preferred): https://github.com/postalsys/bounce-classifier/security/advisories/new.
2. Email: andris@postalsys.com. Encrypt sensitive details if possible (PGP key fingerprint 5D952A46E1D8C931F6364E01DC6C83F4D584D364).

Please provide enough information to evaluate both the defect and its security impact. Reports should include:

1. The affected @postalsys/bounce-classifier version or commit, Node.js version, and relevant configuration.
2. A concise description of the issue and the affected public API or code path (for example text preprocessing and tokenization, model loading, inference, or the public classification API).
3. A minimal, tested reproduction, including steps to run it, expected behavior, and observed behavior.
4. A concrete threat model: attacker control, prerequisites, trust boundary, and resulting impact. Clearly distinguish what your reproduction proves from what you believe might be possible.
5. An explanation of why the issue affects real deployments beyond a deliberately constructed test setup, where this is not obvious.

A suggested fix is welcome but does not replace an explanation of exploitability. A complete real-world exploit is not always necessary, but the report must make a credible security impact clear.

The following generally do not qualify for private security handling unless you can demonstrate an additional, meaningful security boundary crossing:

• Issues that require the attacker to control trusted application code, administrator-only configuration, or the secret they supposedly extract.
• Problems caused solely by application-level misuse, exposed credentials, or insecure deployment choices outside @postalsys/bounce-classifier's control.
• Contrived proof-of-concept setups where the tester controls both sides of a request, without explaining how a separate attacker could trigger the issue.
• Parser quirks, unexpected behavior, and bypasses of internal checks with no demonstrated security impact.
• Speculative findings based only on static analysis or an automated tool's assessment, without a verified reproduction and credible attack scenario.

These may still be valid bugs and may be considered through the normal issue tracker. Please coordinate before making any potentially exploitable details public. Classification as a bug does not guarantee a fix or a particular priority.

Automated analysis and AI tools are welcome as research aids, but the person submitting a report is responsible for verifying its claims. Do not submit bulk, unverified, or speculative AI-generated findings. Test each finding against a supported release and establish the actual security impact. Reports that do not meet the requirements above may be closed without further investigation or individual feedback; they can be resubmitted with stronger evidence.

@postalsys/bounce-classifier is maintained by a small team, and there is no guaranteed response or resolution time. Reports are prioritized based on demonstrated impact, exploitability, affected usage, and available maintenance resources.

A private report does not automatically become a security advisory. Confirmed vulnerabilities may be fixed and disclosed through GitHub Security Advisories; other findings may be closed, deferred, or handled as ordinary bugs. Please do not disclose details of an unresolved, potentially exploitable issue publicly without coordinating with the maintainers.

We do not request or manage CVE identifiers. A report being acknowledged, a bug being fixed, or a pull request being merged does not mean that @postalsys/bounce-classifier has confirmed a security vulnerability or endorsed a CVE assignment. We do not guarantee advisories, CVE identifiers, or public credit for reports. For confirmed vulnerabilities disclosed through an advisory, substantive reporters may be credited if they wish.

In scope: the @postalsys/bounce-classifier source in this repository: preprocessing and tokenization of bounce text, loading of the bundled model, inference, and the public API. Of particular interest are inputs that crash the host process, cause catastrophic regular-expression backtracking, or consume resources out of proportion to their size.

Out of scope:

• Misclassification of a bounce. A wrong category is a model quality issue, not a vulnerability; mislabeled bounces can be submitted at https://bounces.postalsys.com.
• Vulnerabilities in your own application code, including what it does with a classification result.
• Replacing the bundled model with an untrusted one.
• Social-engineering reports.

Thank you for helping keep @postalsys/bounce-classifier and its users safe.