Under-validated ComSpec and cmd.exe resolution in Mutagen projectsGHSA-fwj4-72fm-c93g
GHSA-fwj4-72fm-c93g is a security vulnerability in github.com/mutagen-io/mutagen. A fix is available for github.com/mutagen-io/mutagen — see the affected versions and patch details below.
Real-World Exposure
github.com/mutagen-io/mutagen🐹github.com/mutagen-io/mutagenReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Impact
Mutagen projects offer shell-based execution functionality. On Windows, the shell is resolved using the standard %ComSpec% mechanism, with a fallback to a %PATH%-based search for cmd.exe. While this is the standard practice on Windows systems, it presents somewhat risky behavior.
Firstly, %ComSpec% could, in theory, be set maliciously. Unfortunately, there's not much that can be done to prevent this attack surface, because %ComSpec% is the official mechanism for shell specification on Windows. We can, however, validate that it points to an absolute path, which one would expect for a properly set value.
Secondly, a fallback to a relative cmd.exe path, resolved via %PATH%, could be risky. The risk is largely mitigated by changes in Go 1.19 and later, but prior to that a malicious cmd.exe could been resolved in the current working directory. To mitigate this issue, Mutagen now uses the %SystemRoot% environment variable (also validated to be an absolute path) to resolve cmd.exe in the event that %ComSpec% is not set correctly.
Patches
The problem has been patched in Mutagen v0.16.6 and v0.17.1. Earlier versions of Mutagen are no longer supported and will not be patched. Versions of Mutagen after v0.18.0 will also have the patch merged.
Workarounds
Maintain control of the environment variable settings on your system, in particular the ComSpec environment variable.
References
More information on %ComSpec% can be found online.
More information on Go's PATH-based lookup changes can be found here, here, and here.
A similar issue that was addressed within the Python subprocess module also provides additional discussion.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/mutagen-io/mutagen | all versions | 0.16.6go get github.com/mutagen-io/mutagen@v0.16.6 |
| 🐹Go | github.com/mutagen-io/mutagen | ≥ 0.17.0&&< 0.17.1 | 0.17.1go get github.com/mutagen-io/mutagen@v0.17.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/mutagen-io/mutagen, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/mutagen-io/mutagen to 0.16.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-fwj4-72fm-c93g is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is GHSA-fwj4-72fm-c93g in your dependencies?
Find it across Go, including transitive dependencies.