GHSA-h35f-9h28-mq5c is a medium-severity (CVSS 6.1) CWE-176 vulnerability in setuptools. O3 Security confirms whether GHSA-h35f-9h28-mq5c is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
setuptools: MANIFEST.in exclusion bypass in sdist via Unicode normalization collision (NFC/NFD) on macOS APFS/HFS+
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for GHSA-h35f-9h28-mq5c.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-h35f-9h28-mq5c plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 369,023 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
setuptoolsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
When building a source distribution (python -m build --sdist / setup.py sdist), setuptools' FileList applies MANIFEST.in directives (exclude, global-exclude, recursive-exclude, prune) by matching a compiled glob against on-disk file names byte-for-byte, with no Unicode normalization. On normalization-preserving filesystems (notably macOS APFS and HFS+), a file written in NFD and a MANIFEST.in rule written in NFC refer to the same file but are byte-distinct, so the exclusion silently fails to match. A file the maintainer intended to exclude is then packed into the .tar.gz and, if published, uploaded to the public, immutable PyPI index.
Details
File names in FileList.files come from os.walk (setuptools/_distutils/filelist.py, _find_all_simple), so on APFS a file written NFD is offered to the matcher in NFD, while the MANIFEST.in pattern carries the author's editor form (typically NFC). The matching path performs no canonicalization:
# setuptools/command/egg_info.py (FileList.global_exclude)
def global_exclude(self, pattern):
match = translate_pattern(os.path.join('**', pattern)) # fnmatch.translate -> regex, no NFC/NFD
return self._remove_files(match.match) # byte-level regex over raw os.walk names
A rule written NFC (café = 63 61 66 c3 a9) does not match an on-disk name written NFD (café = 63 61 66 65 cc 81), even though the filesystem treats the two as one file.
A unicodedata.normalize('NFD', ...) helper exists in setuptools/unicode_utils.py (decompose()), but it is never called in the manifest matching path, so neither the pattern nor the walked path is normalized before matching. The only normalization in this area, EggInfoCommand._manifest_normalize, uses filesys_decode (bytes→str decode only, no NFC/NFD) and runs when writing SOURCES.txt, after matching has already occurred.
Impact
MANIFEST.in exclusions are the documented mechanism maintainers use to keep secrets, local configs, and private fixtures out of the published sdist. A non-ASCII excluded file may be published to the public, immutable PyPI index despite the rule — an irreversible disclosure with no visual cue (NFC and NFD forms render identically). Exposure is filesystem-dependent and most relevant on macOS APFS/HFS+, where many maintainers build and publish. Pure-ASCII rules are unaffected.
Proof of concept
With a project containing MANIFEST.in:
global-include *.txt *.json
global-exclude secret_café.txt # rule saved NFC
and an on-disk file secret_café.txt written in NFD, python -m build --sdist packs the secret file into the resulting .tar.gz, while an ASCII control file excluded by the same directive is correctly dropped — isolating the bypass to the NFC-pattern vs. NFD-name mismatch. Reproduced on macOS APFS with setuptools 82.0.1.
Remediation
Normalize both the walked path and each MANIFEST.in pattern to a single canonical form before matching, in both setuptools/command/egg_info.py (FileList) and the vendored setuptools/_distutils/filelist.py. For an exclusion list, err toward excluding more, and document that MANIFEST.in matching is normalization-insensitive on macOS.
Credit
Reported by Tomas Illuminati. Coordinated via CERT/CC VINCE VU#604762.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | setuptools | all versions | 83.0.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for setuptools. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update setuptools to 83.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-h35f-9h28-mq5c 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.
How O3 protects you
O3 pinpoints whether GHSA-h35f-9h28-mq5c is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-h35f-9h28-mq5c. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Frequently Asked Questions
Is GHSA-h35f-9h28-mq5c in your dependencies?
O3 detects GHSA-h35f-9h28-mq5c across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.