PatchSiren cyber security CVE debrief

CVE-2020-25658 Siemens CVE debrief

CVE-2020-25658 is a Bleichenbacher timing attack vulnerability in python-rsa, a pure-Python RSA implementation. The flaw allows an attacker to decrypt portions of RSA-encrypted ciphertext by exploiting timing variations in the RSA decryption API. This vulnerability was originally disclosed in 2020 but was added to the CISA ICS advisory ICSA-24-102-04 on April 9, 2024, as part of a broader security update for Siemens RUGGEDCOM APE1808 devices. The advisory was subsequently modified multiple times through May 13, 2025, to incorporate additional upstream vulnerabilities and remediation guidance. Siemens has issued a vendor fix requiring upgrade to Palo Alto Networks Virtual NGFW V11.1.2-h3 for affected RUGGEDCOM APE1808 deployments configured with this component. The CVSS 3.1 vector indicates network attack vector with low attack complexity, no privileges required, and high confidentiality impact.

Vendor: Siemens
Product: RUGGEDCOM APE1808
CVSS: HIGH 7.5
CISA KEV: Not listed in stored evidence
Original CVE published: 2024-04-09
Original CVE updated: 2025-05-13
Advisory published: 2024-04-09
Advisory updated: 2025-05-13

Who should care

Organizations operating Siemens RUGGEDCOM APE1808 industrial networking devices with Palo Alto Networks Virtual NGFW configurations should prioritize this vulnerability. Security teams responsible for OT/ICS environments, cryptographic implementations, and side-channel attack mitigations should assess exposure. Developers using python-rsa for RSA operations should evaluate migration to constant-time cryptographic libraries.

Technical summary

The python-rsa library implements RSA encryption in pure Python without constant-time operations for decryption, making it vulnerable to Bleichenbacher's million message attack. An attacker with network access to an application using python-rsa's RSA decryption API can send crafted ciphertexts and measure decryption timing to iteratively recover plaintext. The attack exploits the PKCS#1 v1.5 padding oracle created by timing variations in modular exponentiation and padding validation. This vulnerability specifically affects Siemens RUGGEDCOM APE1808 devices when configured with Palo Alto Networks Virtual NGFW, where python-rsa may be used for cryptographic operations. The vendor remediation requires upgrading the NGFW component to version 11.1.2-h3.

Defensive priority

HIGH

Recommended defensive actions

Upgrade Palo Alto Networks Virtual NGFW to V11.1.2-h3 on affected RUGGEDCOM APE1808 devices per vendor guidance
Contact Siemens customer support to obtain patch and update information for affected deployments
Review network segmentation for RUGGEDCOM APE1808 devices to limit exposure of RSA decryption operations
Monitor for anomalous timing patterns in RSA decryption API usage that may indicate exploitation attempts
Apply defense-in-depth controls per CISA ICS recommended practices for industrial control systems

Evidence notes

CVE published 2024-04-09 per CISA CSAF advisory ICSA-24-102-04; modified 2025-05-13. Original python-rsa vulnerability from 2020. Siemens RUGGEDCOM APE1808 affected when configured with Palo Alto Networks Virtual NGFW. Vendor fix requires upgrade to V11.1.2-h3.

Official resources

2024-04-09