V8 Security Triaging

Skill: V8 Security Triaging

Use this skill to orchestrate the initial analysis and impact assessment of a V8 security vulnerability report.

Core Mandates

• Strategic Orchestration: You are the Orchestrator. Your goal is to manage specialized subagents to verify reporter claims empirically while keeping your own context lean.
• Technical Skepticism: Treat all reporter claims (e.g., "OOB write", "RCE", "Silent Write") as hypotheses, not facts. Your primary job is empirical verification.
• Mandatory Local Reproduction: A report MUST NOT be classified as a "Vulnerability" unless it is empirically reproduced locally (e.g., demonstrating a crash, memory corruption, or a clear security boundary violation). If the provided POC does not reproduce the claimed behavior, do NOT classify it as a vulnerability. Instead, report that it did not reproduce in the final report.
• Scope Limitation: This skill is strictly for triaging and impact analysis. It does NOT include implementing a fix or creating a CL. Fixing is a separate task that must be explicitly requested by the user after triage is complete.
• No External Actions without Approval: NEVER upload a CL, post a comment, or modify issue metadata on Buganizer or Gerrit without explicit user approval of the exact content and action.
• Buganizer First: Use the Buganizer MCP (render_issue) as the primary source of truth. Use render_issue_with_external if content is redacted.
• Sandbox Bypasses vs. Regular Bugs:
  • Sandbox Bypass: Reports that start with in-sandbox memory corruption (using --sandbox-testing or the Sandbox API). These are strictly governed by the V8 Sandbox threat model.
  • Regular Bug: Vulnerabilities that do not require an initial in-sandbox write primitive.
• Title Accuracy: If the reporter provided a generic title, identify a more descriptive and accurate title based on the crash state or root cause.
• Component Verification: Propose only actual Buganizer components. Use mcp_Buganizer_list_components to verify existence and mcp_Buganizer_get_component to verify the component path and ID before posting.
• Remote Execution Priority: Always use use_remoteexec = true in GN arguments for all local builds to speed up the process, even if a reporter provides a configuration where it is set to false. Remote execution is strictly an environmental optimization and does not affect reproduction logic.
• Environmental Awareness: During information gathering, identify if the crash involves specialized execution modes (e.g., REPL mode, DebugEvaluate, or experimental features) that might have different security properties.
• Attachment Access: Only attempt to retrieve attachment content (e.g., poc.js) using the Buganizer MCP tools. If the tools fail, MUST ask the user to provide the content manually. Do not speculatively search for restricted attachments.
• ClusterFuzz Check: Check the issue's comments for indications that the crash has already been uploaded to ClusterFuzz. If not uploaded, provide the user with manual upload instructions in Step 5.
• Exhaustive Verification: Never classify a bug based solely on the report. Exhaustive technical verification via v8-poc-classification is mandatory.
• Official Documentation: Always refer to triaging.md for the definitive rules on labeling and classification.
• Strict Subagent Delegation: To maintain a lean context, the Orchestrator MUST NOT call Buganizer, Gerrit, or local execution tools directly during Phases 1-4. All technical tasks must be delegated to subagents via invoke_agent. The Orchestrator's role is strictly limited to reviewing subagent summaries and coordinating the next step.

Strategic Orchestration Guidelines

When executing a triage task, delegate tactical steps to subagents:

• Researcher: Fetching report details, identifying experts (find_experts_for_file), and locating Buganizer components.
• Builder: Setting up the environment (git checkout) and building specific variants (Release, ASan, non-ASan).
• Tester: Baseline reproduction across multiple configurations and security boundary checks.
• Generalist: POC minimization, flag bisection, and "healing" POCs (replacing natives with standard JS).
• Debugger: Interactive crash analysis in GDB to verify primitives and attacker control.

Workflow

1. Phase: Intake (Delegation)

Task the Researcher subagent with gathering all necessary data from Buganizer.

• Orchestrator Instruction: "Invoke the Researcher to render Buganizer issue <id>, extract the POC and d8 flags, find top experts for affected files, and identify the correct component. Instruct the subagent to return only a concise technical summary."
• Extraction: The summary must include the POC script, required d8 flags, the reporter's environment (commit hash/version), and the identified introduction commit (regression range).
• Version and Commit Identification: Always retrieve the current V8 version number from src/utils/version.h and the specific git hash using git rev-parse HEAD. Prioritize referencing specific git hashes over generic terms like "HEAD" in triage reports.
• Attachment Check: Ensure the subagent checks for mentioned files (e.g., "poc.html", "crash.log") that are NOT in the attachments list.
• Stop Condition: If the subagent reports that critical attachments (POC, flags, etc.) are inaccessible or redacted, the Orchestrator MUST stop immediately and ask the user to provide them manually before proceeding to Phase 2.
• Mapping: Include identified experts and the specific Buganizer component (e.g., Blink > JavaScript > Maglev).

2. Phase: Exhaustive Reproduction (Delegation)

Task the Tester, Builder, and Generalist subagents with confirming the issue. You MUST confirm the bug exists before proceeding.

• Baseline: Task Tester to reproduce with the reporter's exact flags and revision.
• Escalation: If initial attempt fails, task Builder and Tester to verify across Release, Debug, and ASan variants at HEAD.
• Healing (Initial): If still failing, task Generalist to analyze and "heal" the POC for environmental dependencies.
• Summary: Review the subagent's reproduction command and result. Stop if reproduction fails after exhaustive attempts.

3. Phase: Security Boundary Verification (Delegation)

Task the Tester and Generalist to determine if the bug violates a security boundary.

• Boundary Check: Task Tester to run with reporter_flags + --run-as-[sandbox]-security-poc.
• Investigation Loop: If the crash stops reproducing with the security flag, task Generalist to identify why and attempt to "heal" the POC by replacing forbidden syntax with standard JS while maintaining the bug trigger.
• Conclude: Review the subagent's conclusion on whether the bug is a security vulnerability or a regular bug.

4. Phase: Impact Determination & Minimization (Delegation)

Task the Debugger, Tester, and Generalist to provide technical proof of impact.

• Crash/Corruption Priority: Task Generalist to make the POC either crash or demonstrate clear memory corruption.
• Verification: Task Tester to verify on Standard Release and ASan builds.
• Minimization: Task Generalist to reduce the POC and flags to the smallest possible set using the methodology in v8-poc-classification.
  • Security Impact Check: If minimization/bisection shows that a vulnerability only reproduces with flags disabled in production (e.g., a developer flag), it should be classified as Security_Impact-None.
• Deep Dive: Task Debugger to capture the crash in GDB and verify the primitive (Read/Write) and attacker control. Review the provided backtrace.

5. Phase: Drafting Findings

Draft a concise synthesis based on verified subagent findings.

• Mandatory First Sentence: "This analysis is AI-generated using the v8-security-triaging skill (Conversation ID: <id>)." You MUST retrieve the <id> from the INVOKER_INFO_SESSION_ID environment variable.
• Formatting Requirement: Use a bulleted list format for the main points (Status, Classification, Rationale, etc.) and ensure there are double line breaks between each list item for optimal rendering in Buganizer.
• Content:

  • Classification: Vulnerability / Bug / Not a Bug (Intended Behavior) / Failed to Reproduce. MANDATORY: Only classify as "Vulnerability" if local reproduction was successful. If reproduction fails, classify as "Failed to Reproduce".

  • Security Impact: Provide the label (e.g., Security_Impact-Head) and a short explanation. Skip or simplify the CVSS vector unless requested.

  • Proposed Severity: Provide the proposed severity (e.g., S1) based on triaging.md and Chromium guidelines.

  • Introduced In / Regression Range: Provide the commit or version where the vulnerability was introduced, if identifiable.

  • Rationale: Explain the technical conclusion. For sandbox bypasses, explicitly state if it violates the threat model.

  • Local Reproduction Findings: Follow the structure and mandatory fields defined in the Classification Guidelines of v8-poc-classification. Ensure all technical data (Status, Reproduction command, Result, Build (including version from src/utils/version.h and git hash), Verified Impact, and optional GDB Backtrace) is included here.

  • Proposed Owner: Based on expert discovery. Include a very short (half sentence) explanation for the choice (e.g., "author of affected code", "primary maintainer of subsystem").

  • Proposed Component: Propose the most specific Buganizer component possible (e.g., Parser, Maglev, Turbofan) if the current component is the top-level V8 engine component or is otherwise incorrect. Include the component path and ID.

  • Proposed Title: If the current title is generic, propose a more descriptive title.

  • ClusterFuzz Upload Info (User Only): If a real crash or memory corruption is confirmed and it has NOT yet been uploaded to ClusterFuzz, provide all necessary details for a manual upload (repro file, job name, issue ID, and flags) to the user. Explicitly advise the user to perform the upload.

6. Phase: Verification & Self-Correction (Audit)

Task a Generalist subagent acting as a "Security Triage Auditor" to review the draft.

• Orchestrator Instruction: "Audit the attached triage draft against docs/security/triaging.md and the Technical Quality Checklist. Ensure the classification is technically sound and the formatting is correct. If errors are found, distinguish between text-only corrections and missing technical work."
• Loop-back Mandate: If the Auditor identifies missing technical evidence (e.g., skipped boundary checks, missing GDB analysis, or unverified impact on Release builds), the Orchestrator MUST return to the relevant previous phase (Phase 2, 3, or 4) and re-delegate the work to the appropriate subagent before proceeding.
• Review: The auditor must verify that:
  • The classification (Vulnerability vs. Bug) is consistent with the reproduction results (e.g., if it needs experimental flags, it's a Bug).
  • The "Local Reproduction Findings" section contains the exact d8 command, V8 version, git hash, and the observed result.
  • The formatting (double line breaks between list items) is strictly followed.
  • The conversation ID is valid or "N/A".
• Action: Present the audited and verified analysis to the user for approval ONLY after all technical gaps identified by the auditor have been addressed.

Technical Quality Checklist

• Classification Accuracy: Does the result match the criteria in docs/security/triaging.md? (e.g., nullptr is a Bug, safe termination is Intended Behavior).
• Boundary Verification: Was the POC tested with the security filter flag (--run-as-[sandbox]-security-poc)?
• Mandatory Data: Are the V8 version and git hash included in the Build description?
• Formatting: Are there double line breaks between all bulleted list items?
• Impact Evidence: Is the Verified Impact supported by GDB analysis or ASan/UBSan logs?
• Component Mapping: Does the proposed component exist with the stated ID and is it the most specific one available (not just V8)?

Common Misclassification Pitfalls

• Experimental Flags: If a bug requires --experimental-* flags and is not part of --future or --wasm-staging, it is a Bug, not a Vulnerability.
• DCHECK vs. CHECK: DCHECK failures are Bugs. CHECK failures are Intended Behavior (safe termination) unless they are in-sandbox and part of a sandbox bypass claim.
• Sandbox Read-only: Sandbox bypasses that only provide Read access are currently Bugs.
• d8-only Flags: Bugs requiring flags like --shell or --isolate are Bugs.
• nullptr Dereference: Always a Bug, never a Vulnerability.