CVE-2024-3862

What it actually does

The MarkStack assignment operator in the JavaScript engine could access uninitialized memory if used in a self-assignment scenario, resulting in memory corruption.

Why it matters to the business

This can cause application instability, crashes, or potential code execution in environments running affected JavaScript or WebAssembly engines, increasing operational risk and remediation urgency for downstream dependents.

How an attack unfolds

An attacker supplies crafted JavaScript that triggers a self-assignment on the MarkStack, causing the engine to read from uninitialized memory which may be leveraged to corrupt state or achieve code execution.

How to fix it

Upgrade bytecodealliance/wasmtime to the fixed commit 666c2554ea0e1728c35aa41178cf235920db888a; for Firefox-based deployments ensure version 125 or later is deployed.

How to confirm the fix worked

Confirm the running binary or package reports the fixed commit hash or version 125+, and test that self-assignment operations no longer trigger memory errors under fuzzing or unit tests.

Typical attack path

1. Deliver malicious JavaScript or WebAssembly content to the target engine
2. Trigger MarkStack self-assignment code path
3. Read or corrupt uninitialized memory
4. Escalate to denial of service or arbitrary code execution

How to detect it

Monitor process crash logs and memory sanitizer reports for patterns involving MarkStack or assignment operations; review application logs for unexpected memory access violations after JavaScript execution.

What your security team should do

• Apply the fixed wasmtime commit or Firefox 125+ immediately across all instances
• Scan build pipelines and dependency manifests for the vulnerable versions
• Enable memory safety mitigations such as ASAN in testing environments until patches are validated