GHSA-H35F-9H28-MQ5C
Vulnerability from github – Published: 2026-07-21 19:09 – Updated: 2026-07-21 19:09Summary
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": [
{
"package": {
"ecosystem": "PyPI",
"name": "setuptools"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "83.0.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-59890"
],
"database_specific": {
"cwe_ids": [
"CWE-176",
"CWE-697"
],
"github_reviewed": true,
"github_reviewed_at": "2026-07-21T19:09:21Z",
"nvd_published_at": "2026-07-08T17:17:27Z",
"severity": "MODERATE"
},
"details": "## Summary\n\nWhen building a source distribution (`python -m build --sdist` / `setup.py sdist`), setuptools\u0027 `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.\n\n## Details\n\nFile 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\u0027s editor form (typically NFC). The matching path performs no canonicalization:\n\n```python\n# setuptools/command/egg_info.py (FileList.global_exclude)\ndef global_exclude(self, pattern):\n match = translate_pattern(os.path.join(\u0027**\u0027, pattern)) # fnmatch.translate -\u003e regex, no NFC/NFD\n return self._remove_files(match.match) # byte-level regex over raw os.walk names\n```\n\nA rule written NFC (`caf\u00e9` = `63 61 66 c3 a9`) does not match an on-disk name written NFD (`caf\u00e9` = `63 61 66 65 cc 81`), even though the filesystem treats the two as one file.\n\nA `unicodedata.normalize(\u0027NFD\u0027, ...)` 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\u2192str decode only, no NFC/NFD) and runs when writing `SOURCES.txt`, after matching has already occurred.\n\n## Impact\n\n`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 \u2014 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.\n\n## Proof of concept\n\nWith a project containing `MANIFEST.in`:\n\n```\nglobal-include *.txt *.json\nglobal-exclude secret_caf\u00e9.txt # rule saved NFC\n```\n\nand an on-disk file `secret_caf\u00e9.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 \u2014 isolating the bypass to the NFC-pattern vs. NFD-name mismatch. Reproduced on macOS APFS with setuptools 82.0.1.\n\n## Remediation\n\nNormalize 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.\n\n## Credit\n\nReported by Tomas Illuminati. Coordinated via CERT/CC VINCE VU#604762.",
"id": "GHSA-h35f-9h28-mq5c",
"modified": "2026-07-21T19:09:21Z",
"published": "2026-07-21T19:09:21Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/pypa/setuptools/security/advisories/GHSA-h35f-9h28-mq5c"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-59890"
},
{
"type": "WEB",
"url": "https://github.com/pypa/setuptools/commit/dd9f436a36486b4cb8a4c70a2321548b0be09b8f"
},
{
"type": "WEB",
"url": "https://github.com/pypa/advisory-database/tree/main/vulns/setuptools/PYSEC-2026-3447.yaml"
},
{
"type": "PACKAGE",
"url": "https://github.com/pypa/setuptools"
},
{
"type": "WEB",
"url": "https://github.com/pypa/setuptools/releases/tag/v83.0.0"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:L/A:N",
"type": "CVSS_V3"
}
],
"summary": "setuptools: MANIFEST.in exclusion bypass in sdist via Unicode normalization collision (NFC/NFD) on macOS APFS/HFS+"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.