Investigate RCE 0-day vulnerability when opening a file

[Copilot]

Investigation: RCE 0-day triggered on file open

Investigated a reported RCE 0-day vulnerability triggered when opening a file. The issue is explicitly not in CI workflows.

Findings

• Extraction path traversal: create_file() in mlar/src/main.rs properly validates with canonicalize + starts_with — not exploitable
• Entry name validation: to_pathbuf() rejects .., absolute paths, null bytes, empty components
• CI script injection: sanitize.yml line 62 has ${{ }} injection in run: block, but explicitly out of scope per problem statement
• cargo audit: ml-dsa 0.0.4 has timing side-channel (RUSTSEC-2025-0144) — not RCE

Most promising vector (unresolved)

The brotli-decompressor crate contains unsafe code in decode.rs that processes attacker-controlled compressed data during archive reading. The old version 2.5.1 (transitive dep via mla v1.4.0 in mlar-upgrader) is particularly suspect. A crafted MLA file with malicious brotli payload could potentially trigger memory corruption in the unsafe decompression path.

Status

• Full codebase security audit
• Dependency vulnerability scan (RustSec, GitHub Advisory DB)
• Unsafe code audit across all crates
• Not completed: Conclusive identification and fix of the specific RCE — ran out of time before auditing the brotli-decompressor unsafe code paths

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• rustsec.org
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)