Junglewise Threat Intelligence

CVE-2024-41996: OpenSSL and Siemens DHE resource exhaustion in public key validation

CVE-2024-41996 · Severity: high · CVSS 7.5 · Published 2024-08-26

Technologies: Siemens RUGGEDCOM RST2428P, Siemens SCALANCE XR-500 family, OpenSSL, Siemens SINEC OS. Vendors: Siemens, OpenSSL.

Executive brief

A vulnerability in the way certain security libraries handle encrypted connections allows a remote attacker to overwhelm a server's processor. By initiating a specific type of secure handshake, an attacker can force the server to perform complex mathematical calculations that consume significant system resources while requiring very little effort from the attacker. This can lead to a denial-of-service (DoS) condition where the server becomes slow or completely unresponsive to legitimate users.

Technical details

The vulnerability, part of the 'D(HE)at' class of attacks, stems from improper validation logic during the Diffie-Hellman (DHE) key exchange. Specifically, when an approved safe prime is used, NIST SP 800-56A Rev 3 allows skipping public key order validation; however, affected libraries like OpenSSL 3.x continue to perform these modular exponentiation calculations (\(1 \equiv A^{(p-1)/2} \bmod p\)) regardless. A remote, unauthenticated attacker can initiate a handshake claiming to only support DHE and provide a large public key, forcing the server to perform asymmetric, CPU-intensive operations. This results in high CPU consumption and potential denial of service. OpenSSL versions up to 3.4.0 are noted as affected, and Siemens has released updates for industrial networking products (SINEC OS V3.3) to mitigate the impact.

Affected products

  • OpenSSL OpenSSL 3.0.0 through 3.4.0
  • Siemens SINEC OS before V3.3
  • Siemens RUGGEDCOM RST2428P before V3.3
  • Siemens SCALANCE XC-300/XR-300/XC-400/XR-500 family before V3.3

Timeline

  • 2024-08-26: advisory: Initial disclosure of CVE-2024-41996 and the D(HE)at attack details.
  • 2026-01-28: patched: Siemens released SINEC OS V3.3 to address the vulnerability in industrial products.

References

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