Copier safe template has arbitrary filesystem write access via directory symlinks when _preserve_symlinks: true
Copier is a library and CLI app for rendering project templates. Prior to version 9.11.2, 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 write to arbitrary directories outside the destination path by using directory a symlink along with `_preserve_symlinks: true` and a generated directory structure whose rendered path is inside the symlinked directory. This way, a malicious template author can create a template that overwrites arbitrary files (according to the user's write permissions), e.g., to cause havoc. Version 9.11.2 patches the issue.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-23986
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 7 Nov 2026, 01:07 UTC · Revision 1
Source evidence
Copier safe template has arbitrary filesystem write access via directory symlinks when _preserve_symlinks: true
core-osv · Original sourcePublished 21 Jan 2026, 22:20 UTC
Copier is a library and CLI app for rendering project templates. Prior to version 9.11.2, 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 write to arbitrary directories outside the destination path by using directory a symlink along with `_preserve_symlinks: true` and a generated directory structure whose rendered path is inside the symlinked directory. This way, a malicious template author can create a template that overwrites arbitrary files (according to the user's write permissions), e.g., to cause havoc. Version 9.11.2 patches the issue.
osv:CVE-2026-23986
Complete source record
{
"id": "1b382e8d4f0c0ef0d2025e59e2d36ade1c4333f4ce351350059bb6fe8bb355e9",
"url": "https://osv.dev/vulnerability/CVE-2026-23986",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "Copier safe template has arbitrary filesystem write access via directory symlinks when _preserve_symlinks: true",
"summary": "Copier is a library and CLI app for rendering project templates. Prior to version 9.11.2, 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 write to arbitrary directories outside the destination path by using directory a symlink along with `_preserve_symlinks: true` and a generated directory structure whose rendered path is inside the symlinked directory. This way, a malicious template author can create a template that overwrites arbitrary files (according to the user's write permissions), e.g., to cause havoc. Version 9.11.2 patches the issue.",
"evidence": "osv:CVE-2026-23986",
"products": [],
"severity": "medium",
"structured": {
"id": "CVE-2026-23986",
"aliases": [
"CVE-2026-23986",
"GHSA-4fqp-r85r-hxqh",
"PYSEC-2026-1272"
],
"metrics": [
{
"type": "CVSS_V4",
"score": "CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/copier-org/copier",
"type": "GIT",
"events": [
{
"introduced": "0"
},
{
"fixed": "b9ee2962b5e0a81b838261b630bd36d0c6c3fa87"
},
{
"fixed": "b3a7b3772d17cf0e7a4481978188c9f536c8d8f6"
}
],
"database_specific": {
"extracted_events": [
{
"cpe": "cpe:2.3:a:copier-org:copier:*:*:*:*:*:python:*:*",
"range": [
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"introduced": "0"
},
{
"fixed": "9.11.2"
}
],
"source": "CPE_RANGE"
},
{
"range": [
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"source": "REFERENCES_COMMIT"
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{
"range": [
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"source": "REFERENCES_TAG",
"original_tag": "v9.11.2"
}
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],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-23986.json"
}
}
],
"modified": "2026-10-28T02:30:48.560103407Z",
"provider": "osv",
"references": [
"https://github.com/copier-org/copier/releases/tag/v9.11.2",
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23986.json",
"https://github.com/copier-org/copier/security/advisories/GHSA-4fqp-r85r-hxqh",
"https://nvd.nist.gov/vuln/detail/CVE-2026-23986",
"https://github.com/copier-org/copier/commit/b3a7b3772d17cf0e7a4481978188c9f536c8d8f6"
],
"provider_metadata": {
"cwe_ids": [
"CWE-61"
],
"cna_assigner": "GitHub_M",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23986.json"
}
},
"related_cves": [
{
"value": "CVE-2026-23986",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 516853,
"published_at": "2026-01-21T22:20:37.72+00:00"
}