R14.1: Session token entropy

Short answer: Session identifiers contain at least 128 bits of cryptosecure random. A guessable session id can be guessed by an attacker.

Group: Auth and sessions. Status: stable. Generated from the rule definitions; do not edit by hand.

Playground: https://brevio.pro/tools/agent-guard-playground?rule=R14.1

What it catches

Session token entropy: session identifiers contain at least 128 bits of cryptosecure random.

Why

A guessable session id can be guessed by an attacker.

A bad example

const sid = Math.random().toString(36);

A good example

const sid = crypto.randomBytes(32).toString('hex');

How it is checked

Nothing yet. No scanner and no slice card checks it: it is a standing rule for authors and reviewers.

How to silence it

A person can silence one finding with brevio-core: ignore R14.1 -- reason on the line or the line above. Without the reason it does not count. An agent cannot silence it: the agent hook and the MCP tools never honour the comment, and a pull request that adds one is reported until a reviewer allows it. Fixing the code is still the better answer.

To change what the rule flags, edit its definition in dev_rules.py or code_rules/__init__.py. That is a code change and is reviewed like one.

R14.2 Password hash modern algorithms
R14.3 Token expiration bounding
R14.4 CSRF token validation
R14.5 No credentials in URLs
Every rule