CVE-2021-41500
📋 TL;DR
An incomplete string comparison vulnerability in cvxopt versions up to 1.2.6 allows attackers to create fake Capsule objects that can crash affected applications. This affects users of cvxopt's cholmod module APIs for linear algebra operations. The vulnerability enables denial of service attacks by exploiting improper object validation.
💻 Affected Systems
- cvxopt
📦 What is this software?
Cvxopt by Cvxopt Project
Fedora by Fedoraproject
⚠️ Risk & Real-World Impact
Worst Case
Complete application crash leading to denial of service for all users of the affected service, potentially disrupting critical mathematical computations or scientific workflows.
Likely Case
Application instability and crashes when processing maliciously crafted inputs through the affected cholmod APIs, causing intermittent service disruptions.
If Mitigated
Minimal impact with proper input validation and error handling in place, though some performance degradation may occur.
🎯 Exploit Status
Exploitation requires constructing specific Capsule objects and calling vulnerable APIs. No public exploit code has been identified in the references.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.2.7
Vendor Advisory: https://github.com/cvxopt/cvxopt/issues/193
Restart Required: Yes
Instructions:
1. Upgrade cvxopt to version 1.2.7 or later using pip: 'pip install --upgrade cvxopt>=1.2.7' 2. Restart any Python processes or services using cvxopt. 3. Verify the upgrade with 'pip show cvxopt'.
🔧 Temporary Workarounds
Input validation wrapper
allWrap vulnerable cholmod API calls with custom validation to check input types before processing
# Python code to wrap vulnerable functions
import cvxopt.cholmod
from functools import wraps
def validate_capsule(func):
@wraps(func)
def wrapper(*args, **kwargs):
# Add custom validation logic here
return func(*args, **kwargs)
return wrapper
# Apply to vulnerable functions
cvxopt.cholmod.diag = validate_capsule(cvxopt.cholmod.diag)
🧯 If You Can't Patch
- Implement strict input validation for all calls to affected cholmod APIs
- Isolate cvxopt usage to trusted environments and restrict access to vulnerable functions
🔍 How to Verify
Check if Vulnerable:
Check cvxopt version with Python: 'import cvxopt; print(cvxopt.__version__)' - if version <= 1.2.6 and cholmod APIs are imported, system is vulnerable.Check Version:
python -c "import cvxopt; print(cvxopt.__version__)"Verify Fix Applied:
After upgrade, verify version is >= 1.2.7 with 'import cvxopt; print(cvxopt.__version__)' and test that cholmod APIs handle edge cases without crashing.📡 Detection & Monitoring
Log Indicators:
- Python tracebacks mentioning cvxopt.cholmod functions
- Application crashes during mathematical computations
- Unexpected termination of Python processes using cvxopt
Network Indicators:
- Unusual patterns of API calls to mathematical computation services
- Increased error rates in applications using cvxopt
SIEM Query:
source="application.logs" AND ("cvxopt.cholmod" OR "cvxopt crash" OR "Python traceback")🔗 References
- https://github.com/cvxopt/cvxopt/issues/193
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CXTPM3DGVYTYQ54OFCMXZVWVOMR7JM2D/
- https://github.com/cvxopt/cvxopt/issues/193
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CXTPM3DGVYTYQ54OFCMXZVWVOMR7JM2D/
