Vulnerability Details

Diffie-Hellman Ephemeral Key Exchange DoS Vulnerability (SSL/TLS, D(HE)ater)

Published: 2021-12-16 10:47:19
CVE Author: NIST National Vulnerability Database

CVSS Base Vector:
AV:N/AC:L/Au:N/C:N/I:N/A:P

severity_vector=CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

severity_origin=NVD

severity_date=2021-11-16 15:36:00 +0000 (Tue, 16 Nov 2021)

Summary:
The remote SSL/TLS server is supporting Diffie-Hellman ephemeral (DHE) Key Exchange algorithms and thus could be prone to a denial of service (DoS) vulnerability.

Detection Method:
Checks the supported cipher suites of the remote SSL/TLS server.

Technical Details:
The Diffie-Hellman Key Agreement Protocol allows remote attackers (from the client side) to send arbitrary numbers that are actually not public keys, and trigger expensive server-side DHE modular-exponentiation calculations, aka a D(HE)ater attack. The client needs very little CPU resources and network bandwidth. The attack may be more disruptive in cases where a client can require a server to select its largest supported key size. The basic attack scenario is that the client must claim that it can only communicate with DHE, and the server must be configured to allow DHE.

Recommendations:
- DHE key exchange should be disabled if no other mitigation mechanism can be used and either elliptic-curve variant of Diffie-Hellman (ECDHE) or RSA key exchange is supported by the clients. The fact that RSA key exchange is not forward secret should be considered. - Limit the maximum number of concurrent connections in e.g. the configuration of the remote server. For Postfix this limit can be configured via 'smtpd_client_new_tls_session_rate_limit' option, for other products please refer to the manual of the product in question on configuration possibilities.

Detection Type:
Remote Banner Unreliable

Solution Type:
Mitigation

NIST (National Institute of Standards and Technology) NVD (National Vulnerability Database)

https://nvd.nist.gov/vuln/detail/CVE-2002-20001

References:

https://www.researchgate.net/profile/Anton-Stiglic-2/publication/2401745_Security_Issues_in_the_Diffie-Hellman_Key_Agreement_Protocol
https://github.com/Balasys/dheater

Severity
Medium
CVSS Score
5.0
Published
2021-12-16
Modified
2021-12-17
Category
Denial of Service

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