R2.6: Constant-time secret comparison

Short answer: Use timingSafeEqual / compare_digest. A normal string compare stops at the first wrong byte, so timing leaks the secret.

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

Playground: https://brevio.pro/tools/agent-guard-playground?rule=R2.6

What it catches

Constant-time secret comparison: use timingSafeEqual / compare_digest.

Why

A normal string compare stops at the first wrong byte, so timing leaks the secret.

A bad example

if (token === expected) ok();

A good example

if (timingSafeEqual(Buffer.from(token), Buffer.from(expected))) ok();

How it is checked

A one-line card in the prompt of a slice that touches matching files (dev_rules.slice_micro_rules).

How to silence it

A person can silence one finding with brevio-core: ignore R2.6 -- 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.

R2.7 Secure cookie & CORS hygiene
R2.8 No unsafe code or HTML sinks
R2.1 Tenant context derivation
R2.2 Tenant-scoped data access
Every rule