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vulnerability CVE-2015-4000

TLS: weakening Diffie-Hellman via Logjam

Synthesis of the vulnerability

An attacker, located as a Man-in-the-Middle, can force the TLS client/server to accept a weak export algorithm, in order to more easily capture or alter exchanged data.
Vulnerable products: Apache httpd, Blue Coat CAS, ProxyAV, ProxySG par Blue Coat, SGOS by Blue Coat, DCFM Enterprise, Brocade Network Advisor, Brocade vTM, Clearswift Email Gateway, Debian, Summit, Fedora, FileZilla Server, FreeBSD, HPE BSM, HPE NNMi, HP Operations, HP-UX, AIX, DB2 UDB, IRAD, Security Directory Server, SPSS Modeler, Tivoli Storage Manager, Tivoli System Automation, Tivoli Workload Scheduler, WebSphere AS Traditional, WebSphere MQ, Juniper J-Series, Junos OS, Junos Pulse, Juniper Network Connect, Juniper SBR, lighttpd, ePO, Firefox, NSS, MySQL Community, MySQL Enterprise, Data ONTAP, Snap Creator Framework, SnapManager, NetBSD, nginx, Nodejs Core, OpenSSL, openSUSE, openSUSE Leap, Solaris, Palo Alto Firewall PA***, PAN-OS, Percona Server, RealPresence Collaboration Server, RealPresence Distributed Media Application, RealPresence Resource Manager, Polycom VBP, Postfix, SSL protocol, Pulse Connect Secure, Puppet, RHEL, JBoss EAP by Red Hat, Sendmail, Slackware, SUSE Linux Enterprise Desktop, SLES, Synology DS***, Synology RS***, Ubuntu, WinSCP.
Severity of this weakness: 2/4.
Consequences of a hack: data reading, data creation/edition.
Hacker's origin: internet server.
Creation date: 20/05/2015.
Revision date: 20/05/2015.
Références of this bulletin: 1610582, 1647054, 1957980, 1958984, 1959033, 1959539, 1959745, 1960194, 1960418, 1960862, 1962398, 1962694, 1963151, 9010038, 9010039, 9010041, 9010044, BSA-2015-005, bulletinjan2016, bulletinjul2015, c04725401, c04760669, c04767175, c04770140, c04773119, c04773241, c04774058, c04778650, c04832246, c04918839, c04926789, CERTFR-2016-AVI-303, CTX216642, CVE-2015-4000, DLA-507-1, DSA-3287-1, DSA-3300-1, DSA-3688-1, FEDORA-2015-10047, FEDORA-2015-10108, FEDORA-2015-9048, FEDORA-2015-9130, FEDORA-2015-9161, FreeBSD-EN-15:08.sendmail, FreeBSD-SA-15:10.openssl, HPSBGN03399, HPSBGN03407, HPSBGN03411, HPSBGN03417, HPSBHF03433, HPSBMU03345, HPSBMU03401, HPSBUX03363, HPSBUX03388, HPSBUX03435, HPSBUX03512, JSA10681, Logjam, NetBSD-SA2015-008, NTAP-20150616-0001, NTAP-20150715-0001, NTAP-20151028-0001, openSUSE-SU-2015:1139-1, openSUSE-SU-2015:1209-1, openSUSE-SU-2015:1216-1, openSUSE-SU-2015:1277-1, openSUSE-SU-2016:0226-1, openSUSE-SU-2016:0255-1, openSUSE-SU-2016:0261-1, openSUSE-SU-2016:2267-1, PAN-SA-2016-0020, PAN-SA-2016-0028, RHSA-2015:1072-01, RHSA-2015:1185-01, RHSA-2015:1197-01, RHSA-2016:2054-01, RHSA-2016:2055-01, RHSA-2016:2056-01, SA111, SA40002, SA98, SB10122, SSA:2015-219-02, SSRT102180, SSRT102254, SSRT102964, SSRT102977, SUSE-SU-2015:1143-1, SUSE-SU-2015:1150-1, SUSE-SU-2015:1177-1, SUSE-SU-2015:1177-2, SUSE-SU-2015:1181-1, SUSE-SU-2015:1181-2, SUSE-SU-2015:1182-2, SUSE-SU-2015:1183-1, SUSE-SU-2015:1183-2, SUSE-SU-2015:1184-1, SUSE-SU-2015:1184-2, SUSE-SU-2015:1185-1, SUSE-SU-2015:1268-1, SUSE-SU-2015:1268-2, SUSE-SU-2015:1269-1, SUSE-SU-2015:1581-1, SUSE-SU-2016:0224-1, SUSE-SU-2018:1768-1, TSB16728, USN-2624-1, USN-2625-1, USN-2656-1, USN-2656-2, VIGILANCE-VUL-16950, VN-2015-007.

Description of the vulnerability

The Diffie-Hellman algorithm is used to exchange cryptographic keys. The DHE_EXPORT suite uses prime numbers smaller than 512 bits.

The Diffie-Hellman algorithm is used by TLS. However, during the negotiation, an attacker, located as a Man-in-the-Middle, can force TLS to use DHE_EXPORT (event if stronger suites are available).

This vulnerability can then be combined with VIGILANCE-VUL-16951.

An attacker, located as a Man-in-the-Middle, can therefore force the TLS client/server to accept a weak export algorithm, in order to more easily capture or alter exchanged data.
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