envoyproxy/envoy

wasm: access log extension point is not thread safe

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#41,672 opened on Oct 23, 2025

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area/wasmbughelp wanted

Description

Access logger instances are shared across all threads, which means log() can be called concurrently. It does not seem that Wasm implementation has proper protection against data races (Wasm runtime assumes single threaded caller I believe).

CC @PiotrSikora @mpwarres

Contributor guide

Tech stack
cppwasm
Domain
backendobservability
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C++ threadingWasm single threaded assumptionEnvoy access logging
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
25
Research direction
Investigate the Wasm access log extension code (likely in source/extensions/wasm/) to identify shared state. Consider adding a mutex or thread local storage to protect concurrent access. Review the existing log() call path and ensure thread safety.