解决Nessus扫描的20007 - SSL Version 2

【高危漏洞】

20007 - SSL Version 2 and 3 Protocol Detection##

Synopsis
The remote service encrypts traffic using a protocol with known weaknesses.

Description
The remote service accepts connections encrypted using SSL 2.0 and/or SSL 3.0. These versions of SSL are affected by several cryptographic flaws, including:

• An insecure padding scheme with CBC ciphers.

• Insecure session renegotiation and resumption schemes.

An attacker can exploit these flaws to conduct man-in-the-middle attacks or to decrypt communications between the affected service and clients.

Although SSL/TLS has a secure means for choosing the highest supported version of the protocol (so that these versions will be used only if the client or server support nothing better), many web browsers implement this in an unsafe way that allows an attacker to downgrade a connection (such as in POODLE). Therefore, it is recommended that these protocols be disabled entirely.

NIST has determined that SSL 3.0 is no longer acceptable for secure communications. As of the date of enforcement found in PCI DSS v3.1, any version of SSL will not meet the PCI SSC's definition of 'strong cryptography'.

See Also
https://www.schneier.com/academic/paperfiles/paper-ssl.pdf
http://www.nessus.org/u?b06c7e95
http://www.nessus.org/u?247c4540
https://www.openssl.org/~bodo/ssl-poodle.pdf
http://www.nessus.org/u?5d15ba70
https://www.imperialviolet.org/2014/10/14/poodle.html
https://tools.ietf.org/html/rfc7507
https://tools.ietf.org/html/rfc7568

Solution
Consult the application's documentation to disable SSL 2.0 and 3.0.
Use TLS 1.1 (with approved cipher suites) or higher instead.

Risk Factor
High

CVSS v3.0 Base Score
7.5 (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N)

CVSS Base Score
7.1 (CVSS2#AV:N/AC:M/Au:N/C:C/I:N/A:N)

Plugin Information:
Published: 2005/10/12, Modified: 2019/03/27

Plugin Output
tcp/389

- SSLv3 is enabled and the server supports at least one cipher.
Explanation: TLS 1.0 and SSL 3.0 cipher suites may be used with SSLv3


Medium Strength Ciphers (> 64-bit and < 112-bit key, or 3DES)

DES-CBC3-SHA Kx=RSA Au=RSA Enc=3DES-CBC(168) Mac=SHA1 

High Strength Ciphers (>= 112-bit key)

AES128-SHA Kx=RSA Au=RSA Enc=AES-CBC(128) Mac=SHA1 
AES256-SHA Kx=RSA Au=RSA Enc=AES-CBC(256) Mac=SHA1 
RC4-MD5 Kx=RSA Au=RSA Enc=RC4(128) Mac=MD5 
RC4-SHA Kx=RSA Au=RSA Enc=RC4(128) Mac=SHA1 

The fields above are :

{OpenSSL ciphername}
Kx={key exchange}
Au={authentication}
Enc={symmetric encryption method}
Mac={message authentication code}
{export flag}

【漏洞解决】
在OpenLDAP Server的配置文件slapd.conf中增加非安全协议的过滤

# vim /etc/openldap/slapd.conf

TLSVerifyClient never
TLSCACertificatePath    /etc/openldap/certs
TLSCACertificateFile    /etc/openldap/certs/cacert.pem
TLSCertificateFile      /etc/openldap/certs/servercert.pem
TLSCertificateKeyFile   /etc/openldap/certs/serverkey.pem
TLSCipherSuite ALL:!TLSv1.1:TLSv1.2:!SSLv2:!SSLv3:!aNULL:!eNULL:!MD5:!MEDIUM:!LOW:!EXPORT:@STRENGTH

如下配置表示允许或不允许使用的协议，例如：!TLSv1.1表示不允许使用TLSv1.1，TLSv1.2表示允许使用。
那么这里的配置表示不允许使用TLSv1.1、SSLv2、SSLv3等协议，允许使用TLSv1.2协议。

ALL:!TLSv1.1:TLSv1.2:!SSLv2:!SSLv3:!aNULL:!eNULL:!MD5:!MEDIUM:!LOW:!EXPORT:@STRENGTH