Security Vulnerability: DHEater aka CVE-2002-20001 / CVE-2022-40735 / CVE-2024-41996

This document (000020510) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Server 12
SUSE Linux Enterprise Server 11

https://www.suse.com/security/cve/CVE-2002-20001.html
https://www.suse.com/security/cve/CVE-2024-41996.html
https://www.suse.com/security/cve/CVE-2022-40735.html

Situation

Security researchers from Balasys have published a new attack on Diffie-Hellman key exchange which allows remote attackers to attack network facing SSL / TLS / HTTPS / SSH services leading to excessive compute time usage even by sending small amounts of network traffic even before authentication.

All applications on SUSE Linux Enterprise are affected that have DHE enabled. The Diffie-Hellman Epheremal key exchange is usually configured by default to provide perfect forward secrecy.

Note that Elliptic Curve Diffie-Hellman is not affected by this problem.

Resolution

There are currently no code fixes as this a protocol level problem.

SUSE continues to monitor if and when cryptographic libraries will develop and implement counter measures in their Diffie-Hellman code and then backport those fixes. Up to then, the DHE key exchange method should be disabled and the Elliptic Curve Diffie-Hellman method being used as a workaround.

SUSE currently recommends to disable the DHE key exchange until technological solution can be found, using methods listed in the "additional information" section. While we use DEFAULT_SUSE as a default cipher set, removing DHE unconditionally could break existing setups so SUSE will not remove this proactively at this time.

Status

Security Alert

Additional Information

Workaround
A workaround is to temporary disable DHE key exchange and only use ECDHE (Elliptic Curve Diffie-Hellman), in SSL / TLS / HTTPS using network services. You need to check if this does not cause interoperability issues.

Apache2:
In the SSL vhost config, add the !kDHE modifier to the use SSLCipherSuite in eg. /etc/apache2/ssl-global.conf or local overriding vhost configs,
example:

    SSLCipherSuite DEFAULT_SUSE:!kDHE

NGINX:

    ssl_ciphers ...:!kDHE;

Postfix:

    tls_medium_cipherlist ...:!kDHE

openssh:
Disable the Diffie-Hellman key exchange methods by adding to or using KexAlgorithms in /etc/ssh.d/sshd_config

KexAlgorithms -diffie-hellman-group1-sha1,diffie-hellman-group1-sha256,diffie-hellman-group14-sha1,diffie-hellman-group14-sha256,diffie-hellman-group15-sha256,diffie-hellman-group15-sha512,diffie-hellman-group16-sha256,diffie-hellman-group16-sha512,diffie-hellman-group17-sha512,diffie-hellman-group18-sha512,diffie-hellman-group-exchange-sha1,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha512

For SLES12 SP5

KexAlgorithms diffie-hellman-group1-sha256,diffie-hellman-group14-sha1,diffie-hellman-group14-sha256,diffie-hellman-group15-sha256,diffie-hellman-group15-sha512,diffie-hellman-group16-sha256,diffie-hellman-group16-sha512,diffie-hellman-group17-sha512,diffie-hellman-group18-sha512,diffie-hellman-group-exchange-sha1,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha512

References:

Disclaimer

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