CVE-2020-25658
📋 TL;DR
CVE-2020-25658 is a timing side-channel vulnerability in python-rsa that allows attackers to perform Bleichenbacher attacks against RSA decryption. This enables partial decryption of ciphertexts encrypted with RSA. Any system using vulnerable versions of python-rsa for RSA decryption operations is affected.
💻 Affected Systems
- python-rsa
📦 What is this software?
Fedora by Fedoraproject
Fedora by Fedoraproject
Fedora by Fedoraproject
Python Rsa by Python Rsa Project
⚠️ Risk & Real-World Impact
Worst Case
Attackers could decrypt sensitive data protected by RSA encryption, potentially exposing confidential information, authentication tokens, or session keys.
Likely Case
Partial decryption of RSA-encrypted data over time through repeated timing measurements, potentially exposing structured data patterns or partial secrets.
If Mitigated
With constant-time RSA decryption implementations, the timing side-channel is eliminated, preventing the attack.
🎯 Exploit Status
Exploitation requires the attacker to have access to make RSA decryption requests and measure timing differences. The attack is well-documented in cryptographic literature.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: python-rsa 4.7 and later
Vendor Advisory: https://github.com/sybrenstuvel/python-rsa/security/advisories/GHSA-8wch-w2g2-8pmc
Restart Required: No
Instructions:
1. Update python-rsa to version 4.7 or later using pip: 'pip install python-rsa>=4.7' 2. Verify the update with: 'pip show python-rsa' 3. Restart any Python applications using the library.
🔧 Temporary Workarounds
Disable RSA decryption
allTemporarily disable RSA decryption functionality if not required
Use alternative RSA library
allSwitch to a different RSA implementation with constant-time operations
🧯 If You Can't Patch
- Implement network-level rate limiting on RSA decryption endpoints
- Use application-level monitoring for abnormal timing patterns in decryption operations
🔍 How to Verify
Check if Vulnerable:
Check python-rsa version with: 'python -c "import rsa; print(rsa.__version__)"' or 'pip show python-rsa'Check Version:
python -c "import rsa; print(rsa.__version__)"Verify Fix Applied:
Verify version is 4.7 or higher: 'python -c "import rsa; print('VULNERABLE' if tuple(map(int, rsa.__version__.split('.'))) < (4,7) else 'PATCHED')"'📡 Detection & Monitoring
Log Indicators:
- Unusually high volume of RSA decryption requests
- Requests with malformed or specially crafted RSA ciphertexts
Network Indicators:
- Repeated RSA decryption requests with timing measurements
- Traffic patterns suggesting timing side-channel attacks
SIEM Query:
source=application_logs AND (rsa_decryption_count > threshold OR rsa_decryption_time_variance > threshold)🔗 References
- https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2020-25658
- https://github.com/sybrenstuvel/python-rsa/issues/165
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2SAF67KDGSOHLVFTRDOHNEAFDRSSYIWA/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/APF364QJ2IYLPDNVFBOEJ24QP2WLVLJP/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QY4PJWTYSOV7ZEYZVMYIF6XRU73CY6O7/
- https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2020-25658
- https://github.com/sybrenstuvel/python-rsa/issues/165
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2SAF67KDGSOHLVFTRDOHNEAFDRSSYIWA/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/APF364QJ2IYLPDNVFBOEJ24QP2WLVLJP/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QY4PJWTYSOV7ZEYZVMYIF6XRU73CY6O7/
