Publish GHSA-85v3-4m8g-hrh6

Author: advisory-database[bot]

advisories/github-reviewed/2026/04/GHSA-85v3-4m8g-hrh6/GHSA-85v3-4m8g-hrh6.json

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+{
+  "schema_version": "1.4.0",
+  "id": "GHSA-85v3-4m8g-hrh6",
+  "modified": "2026-04-01T22:28:49Z",
+  "published": "2026-04-01T22:28:49Z",
+  "aliases": [
+    "CVE-2026-34726"
+  ],
+  "summary": "Copier `_subdirectory` allows template root escape via parent-directory traversal",
+  "details": "### Summary\n\nCopier's `_subdirectory` setting is documented as the subdirectory to use as the template root. However, the current implementation accepts parent-directory traversal such as `..` and uses it directly when selecting the template root.\n\nAs a result, a template can escape its own directory and make Copier render files from the parent directory without `--UNSAFE`.\n\n### Details\n\nThe relevant code path is:\n\n1. the template defines `_subdirectory`\n2. Copier renders that string\n3. `template_copy_root` returns `self.template.local_abspath / subdir`\n4. Copier walks that directory as the template root\n\nRelevant code:\n\n- <https://github.com/copier-org/copier/blob/7aa7021bd73797c982492bac3535515d4484fdb7/copier/_main.py#L1056-L1062>\n- <https://github.com/copier-org/copier/blob/7aa7021bd73797c982492bac3535515d4484fdb7/copier/_template.py#L504-L513>\n\nThe effective sink is:\n\n```python\nsubdir = self._render_string(self.template.subdirectory) or \"\"\nreturn self.template.local_abspath / subdir\n```\n\nThere is no check that the resulting path stays inside the template directory.\n\nThe documentation for `_subdirectory` describes it as:\n\n> Subdirectory to use as the template root when generating a project.\n\nand explains it as a way to separate template metadata from template source code:\n\n<https://github.com/copier-org/copier/blob/7aa7021bd73797c982492bac3535515d4484fdb7/docs/configuring.md#L1582-L1646>\n\nThat description fits values like `template` or `poetry`, but not `..`.\n\n### PoC\n\n#### PoC 1: `_subdirectory: ..` escapes to the parent directory\n\n```sh\nmkdir -p root/template dst\necho 'loot' > root/loot.txt\nprintf '%s\\n' '_subdirectory: ..' > root/template/copier.yml\n\ncopier copy --overwrite root/template dst\nfind dst -maxdepth 3 -type f | sort\ncat dst/loot.txt\n```\n\nExpected output includes:\n\n```text\ndst/loot.txt\ndst/template/copier.yml\nloot\n```\n\nThis shows Copier is rendering from `root/` rather than from `root/template/`.\n\n### Impact\n\nIf a user runs Copier on an untrusted template, that template can change the effective template root and make Copier render files from outside the intended template directory.\n\nPractical impact:\n\n- template-root escape via `..`\n- rendering of parent-directory files that were not meant to be part of the template\n- possible without `--UNSAFE`",
+  "severity": [
+    {
+      "type": "CVSS_V3",
+      "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N"
+    }
+  ],
+  "affected": [
+    {
+      "package": {
+        "ecosystem": "PyPI",
+        "name": "copier"
+      },
+      "ranges": [
+        {
+          "type": "ECOSYSTEM",
+          "events": [
+            {
+              "introduced": "0"
+            },
+            {
+              "fixed": "9.14.1"
+            }
+          ]
+        }
+      ]
+    }
+  ],
+  "references": [
+    {
+      "type": "WEB",
+      "url": "https://github.com/copier-org/copier/security/advisories/GHSA-85v3-4m8g-hrh6"
+    },
+    {
+      "type": "PACKAGE",
+      "url": "https://github.com/copier-org/copier"
+    }
+  ],
+  "database_specific": {
+    "cwe_ids": [
+      "CWE-22"
+    ],
+    "severity": "MODERATE",
+    "github_reviewed": true,
+    "github_reviewed_at": "2026-04-01T22:28:49Z",
+    "nvd_published_at": null
+  }
+}