Florianbuetow Claude Code Repudiation

Repudiation Analysis

Analyze source code for repudiation threats where users can deny having performed actions due to insufficient logging and evidence. Maps to STRIDE R -- violations of the Non-repudiation security property.

Supported Flags

Read ../../shared/schemas/flags.md for the full flag specification. This skill supports all cross-cutting flags including --scope, --depth, --severity, --format, --fix, --quiet, and --explain.

Framework Context

Read ../../shared/frameworks/stride.md, specifically the R - Repudiation section, for the threat model backing this analysis. Key concerns: missing audit logs, log tampering, log injection, insufficient logging detail, log deletion.

Workflow

1. Determine Scope

Parse flags and resolve the target file list per the flags spec. Prioritize files containing security-critical operations:

• Authentication handlers (login, logout, password reset, MFA enrollment)
• Payment processing and financial transaction handlers
• Admin actions and user management endpoints
• Data modification endpoints (create, update, delete on sensitive resources)
• Access control decision points (grant/deny/escalate)
• File upload and download handlers
• The logging infrastructure itself (logger configuration, log sinks, formatters)

2. Analyze for Repudiation Threats

For each in-scope file, apply the Analysis Checklist below. At --depth standard, check each file for logging around critical actions. At --depth deep, trace the full lifecycle of security events to confirm they are captured end-to-end with sufficient detail, and verify log shipping and tamper protection.

3. Report Findings

Output findings per ../../shared/schemas/findings.md using the REPUD ID prefix (e.g., REPUD-001). Set references.stride to "R" on every finding.

Analysis Checklist

Work through these questions against the scoped code. Each "yes" may produce a finding.

1. Missing audit logs on auth events -- Are login successes, login failures, logout, password changes, and MFA events logged with user identity and timestamp? Search for auth handlers that lack logging calls. Auth failures are especially critical -- they indicate attack attempts.
2. Unlogged data modifications -- Are CREATE, UPDATE, and DELETE operations on sensitive data logged? Check ORM hooks, repository methods, and direct database calls for audit trail gaps. Look for model lifecycle callbacks (e.g., after_save, post_save) that should emit audit events but are absent.
3. Missing actor identity in logs -- Do log entries include who performed the action (user ID, session ID, IP address), or do they only record what happened? Search for log.info, logger.warn calls near critical operations and check if user context is passed as structured metadata.
4. Log injection vulnerability -- Can user input be written into log entries unsanitized? Look for user-controlled strings (usernames, query params, form data) passed directly into log formatters, which could inject fake log entries, break log parsing, or enable CRLF injection. Check: logger.info(f"User {username}") without sanitization.
5. Log tampering exposure -- Are logs written to locations the application can also delete or modify? Check if log files are stored in application-writable directories without append-only flags (chattr +a), write-once storage, or external forwarding to a SIEM/log aggregator.
6. Missing failure logging -- Are authorization denials, validation failures, rate limit hits, and error conditions logged? Look for catch blocks, 403/401 responses, and validation rejection paths that silently discard the event without recording what was attempted and by whom.
7. No transaction evidence -- Do financial or legally significant operations produce tamper-evident records? Check for digital signatures, sequence numbers, or immutable audit entries on payment, consent, or contract events. Are transaction IDs generated server-side and logged?
8. Timestamp integrity -- Are log timestamps generated server-side from a trusted clock, or can clients supply their own? Look for client-provided timestamps accepted without validation on audit records. Check for NTP configuration or trusted time sources in infrastructure code.
9. Insufficient log detail -- Do logs capture enough context for forensic reconstruction? Check for: before/after values on updates, affected resource IDs, request metadata (IP, user agent, request ID). Sparse "action completed" entries without context are a forensic gap.
10. Missing centralized aggregation -- Are logs only stored locally on application servers where they can be lost during incidents or rotation? Check for log shipping configuration to external systems: SIEM, ELK, CloudWatch, Datadog, Splunk, or equivalent.
11. Log retention policy gaps -- Is there a defined retention period, or could logs be rotated away before they are needed for incident response? Check log rotation config (logrotate, maxFiles, maxSize) and whether retention aligns with compliance requirements.
12. Selective logging gaps -- Are some code paths logged while equivalent paths are not? For example, if createUser logs but deleteUser does not, or if admin actions are logged but equivalent API actions are not. Look for asymmetric coverage across related handlers.

Pragmatism Notes

• Small internal tools and prototypes may not need comprehensive audit logging. Scale expectations to the application's threat model and regulatory context.
• The presence of a logging framework does not mean critical actions are logged. Verify that security-relevant events specifically have log calls, not just general application logging.
• Log injection severity depends on the log consumer. If logs feed a SIEM with automated alerting, injecting fake entries is high severity. If logs are only read by humans in text files, it is medium.
• Centralized log aggregation is an infrastructure concern. If the codebase is application-only with no infrastructure code, note the gap but do not rate it above low.
• Distinguish between application logs (general debugging) and audit logs (security evidence). The absence of audit-specific infrastructure is a stronger finding than missing debug logs.

What to Look For

Concrete code patterns and grep heuristics to surface repudiation risks:

• Auth handlers without logging: Functions matching login, authenticate, signIn, register, resetPassword, changePassword that do not contain calls to log, logger, audit, emit, or track. Grep: (login|signIn|authenticate|register) then verify adjacent logging.
• CRUD without audit: Database operations (save(), .create(, .update(, .delete(, INSERT, UPDATE, DELETE) in handlers with no adjacent logging call within 5-10 lines. Grep: \.(save|create|update|delete|destroy)\( and check surrounding context.
• Raw user input in logs: logger.info(f"User {username}"), console.log(req.body), log.info("Query: " + userInput) -- any pattern where unsanitized input flows into log formatting. Grep: log\w*\.(info|warn|error|debug)\(.*req\.(body|params|query|headers).
• Catch blocks that swallow: except Exception: pass, catch (e) {}, catch (e) { return; }, .catch(() => {}) -- error handlers with no logging. Grep: catch.*\{\s*\}|except.*:\s*pass.
• Local-only log config: Log configuration writing only to file://, ./logs/, or stdout without forwarding. Absence of log shipping libraries (winston-transport, fluent-logger, logstash, sentry, @google-cloud/logging).
• Missing before/after values: Update operations that log "record updated" without capturing the previous and new state. Check for absence of old_value, previous, before, diff in log payloads near update handlers.
• No request correlation: Absence of request ID or correlation ID in logs, making it impossible to trace a single user action across multiple log entries. Search for requestId, correlationId, traceId, x-request-id in logging middleware.

Output Format

Each finding must conform to ../../shared/schemas/findings.md.

id:          REPUD-<NNN>
severity:    critical | high | medium | low
confidence:  high | medium | low
location:    file, line, function, snippet
description: What the repudiation risk is and what actions can be denied
impact:      What accountability is lost and what forensic gaps result
fix:         Concrete remediation with diff when possible
references:
  stride: "R"
  cwe:    CWE-778 (Insufficient Logging), CWE-117 (Log Injection), or relevant CWE
metadata:
  tool:      repudiation
  framework: stride
  category:  R

Severity Guidelines for Repudiation

Common CWE References

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