N/A

CVSS Score

-

CVSS Score

Basic Information

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CVE-2025-55214

CVE-2025-55214: Copier's safe template has filesystem write access outside destination path

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 write files outside the destination path where a project shall be generated or updated. This is possible when rendering a generated directory structure whose rendered path is either a relative parent path or an absolute path. Constructing such paths is possible using Copier's builtin pathjoin Jinja filter and its builtin _copier_conf.sep variable, which is the platform-native path separator. 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.

Write access via generated relative path

Reproducible example:

echo "foo" > forbidden.txt
mkdir src/
echo "bar" > "src/{{ pathjoin('..', 'forbidden.txt') }}"
uvx copier copy src/ dst/
cat forbidden.txt

Write access via generated absolute path

Reproducible example:

POSIX:

# Assumption: The current working directory is `/tmp/test-copier-vulnerability/`
echo "foo" > forbidden.txt
mkdir src/
echo "bar" > "src/{{ pathjoin(_copier_conf.sep, 'tmp', 'test-copier-vulnerability', 'forbidden.txt') }}"
uvx --from copier python -O -m copier copy --overwrite src/ dst/
cat forbidden.txt

Windows (PowerShell):

# Assumption: The current working directory is `C:\Users\<user>\Temp\test-copier-vulnerability`
echo "foo" > forbidden.txt
mkdir src
Set-Content -Path src\copier.yml @'
drive:
  type: str
  default: "C:"
  when: false
'@
echo "bar" > "src\{{ pathjoin(drive, 'Users', '<user>', 'Temp', 'test-copier-vulnerability', 'forbidden.txt') }}"
uvx --from copier python -O -m copier copy --overwrite src dst
cat forbidden.txt

Miggo Vulnerability Database

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CVE-2025-55214

CVE-2025-55214:

N/A

CVSS Score

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
copier	pip	>= 7.1.0, < 9.9.1	9.9.1

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The analysis of the provided patch commit fdbc0167cc22780b497e4db176feaf6f024757d6 clearly indicates that the vulnerability lies within the _render_template method of the Worker class in copier/_main.py. The vulnerability is a classic path traversal issue. The copier tool generates projects from templates, and part of this process involves rendering file and directory names from the template. The _render_template function iterates through the template files, determines the destination path for each file, and writes the rendered content.

The core of the vulnerability is the lack of validation on the generated destination path (dst_relpath). A malicious template could use Jinja2 templating to construct a path that traverses up from the destination directory (e.g., ../.ssh/authorized_keys) or points to an absolute location on the filesystem. When copier processes this template, it would write a file to that malicious path, potentially overwriting critical system files or user data.

The patch addresses this directly by adding a security check right before any file operations occur. It uses pathlib.Path.resolve() to get the canonical absolute path of the destination and then checks if this path is still within the current working directory (which copier sets to the user-specified destination directory). If the path is outside, it raises a ForbiddenPathError, preventing the write operation. The changes to the _pathjoin function are a secondary hardening measure, but the primary, exploitable flaw is the missing check in _render_template.

Vulnerable functions

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Vulnerability Intelligence
Miggo AI

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WAF Protection Rules

WAF Rule

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Reasoning

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