CVE-2025-27607: Python JSON Logger RCE Vulnerability

CVE-2025-27607 Overview

Python JSON Logger, a popular JSON Formatter for Python Logging, was found vulnerable to Remote Code Execution (RCE) through a dependency confusion attack involving a missing package. Between December 30, 2024 and March 4, 2025, the library referenced a development dependency (msgspec-python313-pre) that had been deleted by its owner, leaving the package name available for registration by malicious actors.

Critical Impact

Any user who installed Python JSON Logger's development dependencies on Python 3.13 using pip install python-json-logger[dev] during the vulnerable period could have been exposed to arbitrary code execution if a malicious actor had claimed the abandoned package name.

Affected Products

• nhairs python_json_logger versions prior to 3.3.0
• Development installations using python-json-logger[dev] on Python 3.13
• CI/CD pipelines installing development dependencies during the vulnerable window

Discovery Timeline

• 2025-03-07 - CVE-2025-27607 published to NVD
• 2025-07-01 - Last updated in NVD database

Technical Details for CVE-2025-27607

Vulnerability Analysis

This vulnerability represents a classic dependency confusion or dependency hijacking attack vector within the Python package ecosystem. The core issue stems from the Python JSON Logger project referencing msgspec-python313-pre as a development dependency for Python 3.13 support. When the original package owner deleted this dependency from PyPI, the package name became orphaned and available for re-registration.

An attacker could have claimed this abandoned package name and uploaded a malicious version containing arbitrary code. Since Python's pip installer automatically executes setup.py during package installation, any code within a malicious replacement package would run with the privileges of the installing user. This is particularly dangerous in automated CI/CD environments where development dependencies are frequently installed.

Root Cause

The root cause is classified under CWE-829 (Inclusion of Functionality from Untrusted Control Sphere). The vulnerability arose from:

1. A dependency on an external package (msgspec-python313-pre) that was outside the project maintainer's control
2. The package owner deleting the dependency without coordinating with downstream projects
3. PyPI's policy allowing deleted package names to be re-registered after a period of time
4. Development dependencies being specified without version pinning or integrity verification

Attack Vector

The attack vector requires network access and user interaction (installation of development dependencies). An attacker would need to:

1. Identify the abandoned package name on PyPI
2. Register the package name under their control
3. Upload a malicious package containing arbitrary Python code in setup.py or package initialization
4. Wait for victims to install development dependencies

The following patches were applied to address Python 3.13 support and remove the vulnerable dependency reference:

     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.13",
     "Topic :: System :: Logging",
     "Typing :: Typed",
 ]

Source: GitHub Commit

 [project]
 name = "python-json-logger"
-version = "3.2.0"
+version = "3.2.1"
 description = "JSON Log Formatter for the Python Logging Package"
 authors = [
     {name = "Zakaria Zajac", email = "zak@madzak.com"},

Source: GitHub Commit

Detection Methods for CVE-2025-27607

Indicators of Compromise

• Presence of msgspec-python313-pre package in installed dependencies
• Unexpected network connections or process spawns during pip installation
• Anomalous Python processes executing during CI/CD pipeline runs
• Suspicious entries in pip installation logs showing msgspec-python313-pre

Detection Strategies

• Audit installed Python packages using pip list or pip freeze to identify msgspec-python313-pre
• Implement Software Composition Analysis (SCA) tools to scan for known vulnerable dependencies
• Review CI/CD logs for any package installations occurring between December 30, 2024 and March 4, 2025
• Use package hash verification with pip install --require-hashes for critical installations

Monitoring Recommendations

• Enable verbose pip logging in CI/CD pipelines to capture all package installation activity
• Implement dependency lockfiles (requirements.txt with hashes or poetry.lock) to prevent dependency confusion
• Monitor PyPI package registrations for packages matching your development dependencies
• Set up alerts for new package installations in production environments

How to Mitigate CVE-2025-27607

Immediate Actions Required

• Upgrade Python JSON Logger to version 3.3.0 or later immediately
• Audit systems for the presence of msgspec-python313-pre package and remove if found
• Review CI/CD pipeline logs from December 30, 2024 to March 4, 2025 for anomalous activity
• Regenerate credentials and rotate secrets on any system that installed development dependencies during the vulnerable period

Patch Information

The vulnerability has been resolved in Python JSON Logger version 3.3.0. The fix removes the reference to the abandoned msgspec-python313-pre package and properly handles Python 3.13 support. Users should upgrade using:

pip install --upgrade python-json-logger>=3.3.0

For detailed information about the security fix, refer to the GitHub Security Advisory.

Workarounds

• Avoid installing development dependencies ([dev] extras) in production environments
• Use dependency pinning with exact versions and hash verification
• Consider using a private PyPI mirror with curated packages for enterprise environments
• Implement namespace prefixing for internal packages to prevent dependency confusion attacks

# Recommended: Install with hash verification
pip install python-json-logger==3.3.0 --require-hashes -r requirements.txt

# Generate hash-pinned requirements
pip-compile --generate-hashes requirements.in -o requirements.txt

# Audit installed packages for vulnerable dependency
pip list | grep -i msgspec