User/saulg/fuzzer by richiemsft · Pull Request #325 · microsoft/mxc

richiemsft · 2026-05-15T20:50:57Z

📖 Description

Adds continuous fuzzing infrastructure for MXC's config-parsing surface using cargo-fuzz (libFuzzer) + OneFuzz.

What's included:

3 fuzz targets: config_parser, base64_decode, validator
Seed corpus derived from existing test configs and examples
Azure Pipeline (Fuzz.Build.yml) with daily cron schedule on main
OneFuzzConfig.json with ADO bug routing to Tessera area path
Documentation in docs/fuzzing.md and src/fuzz/README.md

Pipeline behavior:

trigger: none / pr: none — only runs on daily cron (00:00 UTC)
Builds with AddressSanitizer on Windows x64
Stages drop directory and submits to OneFuzz

🔍 Validation

All 3 fuzz targets run locally on macOS (nightly toolchain) without crashes
config_parser: ~959K runs in 11s ✅
base64_decode: ~1.3M runs in 11s ✅
validator: ~893K runs in 11s ✅
YAML validated as syntactically correct
OneFuzzConfig paths aligned with pipeline staging layout

✅ Checklist

Signed the Contributor License Agreement
Linked to an issue
Updated documentation (if applicable)
Updated Copilot instructions (if build, architecture, or conventions changed)

📋 Issue Type

New feature

Introduces an `mxc_fuzz` crate at `src/fuzz/` with three libFuzzer targets that cover the attacker-influenced JSON / base64 config surface consumed by `wxc-exec` and `lxc-exec`: - `config_parser`: feeds raw JSON into `load_mxc_request`. - `base64_decode`: same entry point with `is_base64 = true` to cover the SDK-supplied wire format end to end. - `validator`: parses, then runs successful one-shot requests through `validate_common`. The crate is excluded from the parent Cargo workspace so `libfuzzer-sys` and the nightly-only `-Z sanitizer=address` flag are only pulled in when fuzzing. Seed corpora are curated one-per-shape from `test_configs/` (26 / 26 / 11 files). OneFuzz expands the corpus across daily runs. Local smoke test on Windows x64 with nightly Rust + ASAN: all three targets compile and run cleanly with no findings against the seed corpus (~6k-28k exec/s, 81-86 edges of coverage on the parse target). Platform coverage: targets are pure Rust (`wxc_common`) and are cross-platform, so the same source compiles on Linux / macOS. We run them under OneFuzz on Windows only because (a) OneFuzz supports only Windows, Ubuntu, AzureLinux3, and TKO -- macOS is not a supported OneFuzz platform, and (b) for these parser targets the bugs are platform-independent, so a single OS gives full coverage of the relevant code paths. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- `src/fuzz/OneFuzzConfig.json`: manifest for the three libFuzzer targets. Routing fields (Owners, AssignedTo, NotificationEmail, Project, AreaPath, IterationPath) are placeholders pending DRI input; they can be filled in without rebuilding any code. Validate with `oip.exe validate` before the first submission. - `.azure-pipelines/templates/Fuzz.Build.Job.yml`: 1ES PT job that installs nightly Rust + cargo-fuzz, builds with AddressSanitizer, stages the OneFuzz drop directory (per-fuzzer subdir with .exe + ASAN runtime DLL + seed corpus), publishes the drop as a pipeline artifact, and submits via `onefuzz-task@0`. Submission is skipped on PR runs. - `.azure-pipelines/Fuzz.Build.yml`: top-level pipeline. `pr: none`, `trigger: none`, daily 00:00 UTC cron on `main`. Extends the 1ES Unofficial template (no ESRP signing -- the binaries are ASAN- instrumented and only ever consumed by OneFuzz). - `docs/fuzzing.md` and `src/fuzz/README.md`: how to run targets locally, minimize the corpus, and triage bugs filed by OneFuzz. Cargo registry stays pointed at Mxc-Azure-Feed in CI so all crate sources still come from the internal feed; only the rustc/cargo binaries come from rustup nightly. A TODO is left to migrate to a Microsoft-published nightly via msrustup once one is available. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Reverts to trigger: none before merge to main; bring-up only. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Adds a fuzzing setup to MXC focused on the attacker-influenced config parsing/validation surface in wxc_common, with local cargo-fuzz harnesses and a scheduled Azure Pipelines job that stages and submits fuzzers to OneFuzz.

Changes:

Introduces a standalone mxc_fuzz crate (src/fuzz/) with 3 libFuzzer targets (config_parser, base64_decode, validator) and curated seed corpora.
Adds a daily scheduled Azure Pipelines definition + job template to build the fuzzers with AddressSanitizer and submit to OneFuzz.
Adds end-user documentation for local and CI fuzzing workflows.

Reviewed changes

Copilot reviewed 74 out of 74 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/fuzz/README.md	Local usage docs for `cargo-fuzz` targets and artifacts/corpus handling.
src/fuzz/OneFuzzConfig.json	OneFuzz job manifest describing 3 fuzzing jobs and ADO routing.
src/fuzz/fuzz_targets/validator.rs	Fuzz target that parses input and runs `validate_common` for one-shot requests.
src/fuzz/fuzz_targets/config_parser.rs	Fuzz target for `load_mxc_request` with raw JSON input.
src/fuzz/fuzz_targets/base64_decode.rs	Fuzz target for `load_mxc_request` with base64-encoded input.
src/fuzz/corpus/validator/basic_lpac.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/basic_lxc.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/basic_permissive.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/basic_processcontainer.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/containment_process_intent.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/hello_world_v050.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/hyperlight_fs.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/hyperlight_hello.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/isolation_session_filesystem.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/isolation_session_hello.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/isolation_session_state_aware_exec_basic.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/isolation_session_state_aware_provision.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/isolation_session_state_aware_stop.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/lxc_filesystem_test.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/microvm_error.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/microvm_hello.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/microvm_timeout.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/network_default_test.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/network_firewall_test.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/rejected_version_too_old.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/windows_sandbox_echo.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/windows_sandbox_powershell.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/windows_sandbox_timeout.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/wslc_custom_registry.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/wslc_filesystem.json	Seed corpus input (validator target).
src/fuzz/corpus/validator/wslc_python_hello.json	Seed corpus input (validator target).
src/fuzz/corpus/config_parser/basic_lpac.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/basic_lxc.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/basic_permissive.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/basic_processcontainer.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/containment_process_intent.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/hello_world_v050.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/hyperlight_fs.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/hyperlight_hello.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/isolation_session_filesystem.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/isolation_session_hello.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/isolation_session_state_aware_exec_basic.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/isolation_session_state_aware_provision.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/isolation_session_state_aware_stop.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/lxc_filesystem_test.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/microvm_error.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/microvm_hello.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/microvm_timeout.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/network_default_test.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/network_firewall_test.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/rejected_version_too_old.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/windows_sandbox_echo.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/windows_sandbox_powershell.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/windows_sandbox_timeout.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/wslc_custom_registry.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/wslc_filesystem.json	Seed corpus input (config_parser target).
src/fuzz/corpus/config_parser/wslc_python_hello.json	Seed corpus input (config_parser target).
src/fuzz/corpus/base64_decode/basic_lxc.b64.txt	Seed corpus input (base64_decode target).
src/fuzz/corpus/base64_decode/basic_processcontainer.b64.txt	Seed corpus input (base64_decode target).
src/fuzz/corpus/base64_decode/empty.txt	Seed corpus input (base64_decode target).
src/fuzz/corpus/base64_decode/hello_world_v050.b64.txt	Seed corpus input (base64_decode target).
src/fuzz/corpus/base64_decode/invalid_chars.txt	Seed corpus input (base64_decode target).
src/fuzz/corpus/base64_decode/isolation_session_hello.b64.txt	Seed corpus input (base64_decode target).
src/fuzz/corpus/base64_decode/microvm_hello.b64.txt	Seed corpus input (base64_decode target).
src/fuzz/corpus/base64_decode/padding_only.txt	Seed corpus input (base64_decode target).
src/fuzz/corpus/base64_decode/unpadded.txt	Seed corpus input (base64_decode target).
src/fuzz/corpus/base64_decode/valid_hello.txt	Seed corpus input (base64_decode target).
src/fuzz/corpus/base64_decode/windows_sandbox_echo.b64.txt	Seed corpus input (base64_decode target).
src/fuzz/Cargo.toml	Defines `mxc_fuzz` crate dependencies and fuzz target bins.
src/fuzz/.gitignore	Ignores fuzz-specific build outputs, artifacts, and coverage.
src/Cargo.toml	Excludes `src/fuzz` from the Rust workspace.
docs/fuzzing.md	End-to-end documentation for fuzzing locally and via the CI pipeline.
.azure-pipelines/templates/Fuzz.Build.Job.yml	Pipeline job template to build ASAN fuzzers and stage a OneFuzz drop.
.azure-pipelines/Fuzz.Build.yml	Scheduled daily pipeline definition to run the fuzz build + submit stage.

Remove branch-trigger used during bring-up validation. The pipeline will only run on the daily cron schedule (00:00 UTC on main). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- OneFuzzConfig.json: Update FuzzerExe, JobDependencies, and Seeds paths to include target subdirectory prefix (matches pipeline staging layout: <target>/<exe>, <target>/corpus) - OneFuzzConfig.json: Replace TODO placeholders with real ADO routing (Project: OS, AreaPath: OS\Windows Client and Services\WinPD\ AgOS-Agentic Platform\Agent Runtime\Tessera) - README.md: Fix relative paths (already cd'd into src/fuzz) - docs/fuzzing.md: Fix artifact paths to be relative to src/fuzz Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

bbonaby · 2026-05-22T03:16:57Z

+# Nightly Rust toolchain: cargo-fuzz requires `-Z sanitizer=address`, which
+# only nightly accepts. The Mxc-Azure-Feed (`ms-prod-*`) toolchains are
+# stable-only today, so we install nightly via `rustup-init` here.
+# TODO(SFI): switch to a Microsoft-published nightly via msrustup once one
+# is available in Mxc-Azure-Feed; until then keep cargo registry pointed at
+# Mxc-Azure-Feed so all *crate* sources still come from the internal feed.


question: Is this something I need to add? I can check and get back to you

unsure, haven't been able to test the azure side since in order to generate the pipeline the code has to be check in. I couldn't reference a non checked in file.

all good, lets check it in so you can try it out. There is a way to do it without having to check it in though if I recall but it's ok lets get it in.

- Remove bring-up branch comment from Fuzz.Build.yml (bbonaby) - Use test_configs/ as seed corpus for config_parser and validator targets instead of maintaining duplicated files in src/fuzz/corpus/ (bbonaby) - Keep src/fuzz/corpus/base64_decode/ for pre-encoded seeds - Update pipeline staging to copy from test_configs/*.json - Enhance validator fuzz target to call runner-specific validate_runner based on containment backend (bbonaby). NanVix always available; Hyperlight and IsolationSession behind opt-in features. - Build validator target with --features hyperlight,isolation_session in CI - Update README and docs/fuzzing.md to reflect new corpus source Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The CodexRequest field is named containment, not containment_backend. The fuzz target was failing to build with E0609. Verified locally by running the validator target for 30s under cargo-fuzz (485k runs, no findings). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

bbonaby · 2026-05-22T22:17:33Z

@@ -0,0 +1,55 @@
+# mxc_fuzz


suggestion: Might be worth it for us to have a table at the bottom with what each base64_decode relates to since they won't be human readable

bbonaby · 2026-05-22T22:19:03Z

+# Nightly Rust toolchain: cargo-fuzz requires `-Z sanitizer=address`, which
+# only nightly accepts. The Mxc-Azure-Feed (`ms-prod-*`) toolchains are
+# stable-only today, so we install nightly via `rustup-init` here.
+# TODO(SFI): switch to a Microsoft-published nightly via msrustup once one
+# is available in Mxc-Azure-Feed; until then keep cargo registry pointed at
+# Mxc-Azure-Feed so all *crate* sources still come from the internal feed.


all good, lets check it in so you can try it out. There is a way to do it without having to check it in though if I recall but it's ok lets get it in.

richiemsft and others added 2 commits May 15, 2026 13:35

Copilot AI review requested due to automatic review settings May 15, 2026 20:50

Copilot started reviewing on behalf of richiemsft May 15, 2026 20:53 View session

Temporarily trigger Fuzz pipeline on user/saulg/Fuzzer pushes

2a5f3b7

Reverts to trigger: none before merge to main; bring-up only. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot AI reviewed May 15, 2026

View reviewed changes

Comment thread .azure-pipelines/templates/Fuzz.Build.Job.yml Outdated

Comment thread src/fuzz/OneFuzzConfig.json

Comment thread src/fuzz/OneFuzzConfig.json

Comment thread src/fuzz/README.md Outdated

Comment thread src/fuzz/README.md Outdated

Comment thread docs/fuzzing.md Outdated

Richie Gomez and others added 3 commits May 18, 2026 11:10

Revert trigger to none for merge to main

1738d40

Remove branch-trigger used during bring-up validation. The pipeline will only run on the daily cron schedule (00:00 UTC on main). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Merge branch 'main' into user/saulg/Fuzzer

c3a4d37

richiemsft marked this pull request as ready for review May 18, 2026 18:26

richiemsft added 3 commits May 18, 2026 14:38

Merge branch 'main' into user/saulg/Fuzzer

f0e936e

Merge branch 'main' into user/saulg/Fuzzer

d344932

Merge branch 'main' into user/saulg/Fuzzer

77f0e4f

bbonaby reviewed May 22, 2026

View reviewed changes

Richie Gomez and others added 2 commits May 22, 2026 09:47

bbonaby approved these changes May 22, 2026

View reviewed changes

richiemsft merged commit cf9721d into main May 22, 2026
18 checks passed

richiemsft deleted the user/saulg/Fuzzer branch May 22, 2026 22:40

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User/saulg/fuzzer#325

User/saulg/fuzzer#325
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richiemsft commented May 15, 2026 •

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📖 Description

🔍 Validation

✅ Checklist

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richiemsft commented May 15, 2026 •

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