cbcvebase.
CVE-2015-4000
published 2015-05-21

CVE-2015-4000: The TLS protocol 1.2 and earlier, when a DHE_EXPORT ciphersuite is enabled on a server but not on a client, does not properly convey a DHE_EXPORT choice, which…

PriorityP351low3.7CVSS 3.1
AVNACHPRNUINSUCNILAN
EXPLOIT
EPSS
99.86%
100.0th percentile
The TLS protocol 1.2 and earlier, when a DHE_EXPORT ciphersuite is enabled on a server but not on a client, does not properly convey a DHE_EXPORT choice, which allows man-in-the-middle attackers to conduct cipher-downgrade attacks by rewriting a ClientHello with DHE replaced by DHE_EXPORT and then rewriting a ServerHello with DHE_EXPORT replaced by DHE, aka the "Logjam" issue.

Affected

50 ranges· showing 25
VendorProductVersion rangeFixed in
appleios
appleiphone_os<= 8.3
applemac_os_x<= 10.10.3
appleos_x_yosemite_v10.10.4_and_security_update_2015-005
canonicalubuntu_linux
canonicalubuntu_linux
canonicalubuntu_linux
canonicalubuntu_linux
debiandebian_linux
debiandebian_linux
debiannss< nss 2:3.19.1-1 (bookworm)nss 2:3.19.1-1 (bookworm)
debianopenjdk-8< nss 2:3.19.1-1 (bookworm)nss 2:3.19.1-1 (bookworm)
debianopenssl< nss 2:3.19.1-1 (bookworm)nss 2:3.19.1-1 (bookworm)
geddyjsgeddy>= 0 < 13.0.813.0.8
hphp-ux
ibmcontent_manager
mozillafirefox
mozillafirefox
mozillafirefox>= 0 < 39.0+build5-0ubuntu0.14.04.139.0+build5-0ubuntu0.14.04.1
mozillafirefox_esr
mozillafirefox_os
mozillanetwork_security_services
mozillanss>= 0 < 2:3.19.1-12:3.19.1-1
mozillanss>= 0 < 2:3.19.1-12:3.19.1-1
mozillanss>= 0 < 2:3.19.1-12:3.19.1-1

Detection & IOCsextracted from sources · hover to see the quote

  • Detect TLS ClientHello packets where DHE_EXPORT ciphersuites are being negotiated — a server supporting DHE_EXPORT ciphers is exploitable as a downgrade target
  • Flag TLS handshakes where DH parameters are 512 bits (export-grade); the MITM rewrites ClientHello replacing DHE with DHE_EXPORT and ServerHello replacing DHE_EXPORT with DHE
  • Monitor for use of pre-computed weak DH primes associated with Apache 2.1.5–2.4.7 and OpenSSL default parameters, which enable 'compute once, use many' offline decryption
  • Inspect TLS handshakes for the DHE_EXPORT downgrade + TLS False Start combination: server supports DHE_EXPORT or 512-bit DHE params AND client uses TLS False Start extension
  • Detect abnormally long TLS handshake durations (several minutes) which may indicate an active MITM computing the 512-bit DH connection key in real time during the handshake
  • Check server TLS configuration for presence of DHE_EXPORT cipher suites in the enabled cipher list; application-specific config may re-enable export ciphers even when the library default excludes them
  • ·NSS versions shipped with RHEL 4, 5, 6, and 7 accepted 512-bit DHE parameters prior to the fix; the fix raises the minimum to 1023 bits (nss-3.19.1)
  • ·OpenSSL packages in RHEL 6 and 7 do not include DHE_EXPORT in the DEFAULT cipher list, but application-level configuration can override this and re-enable export ciphers
  • ·Java JDK implementations (OpenJDK, Oracle JDK, IBM JDK) previously accepted 512-bit (or even 256-bit for IBM) DH parameters; the jdk.tls.disabledAlgorithms security property controls the minimum key size
  • ·openssl097a (RHEL 5), openssl098e (RHEL 6/7), and openssl for JBoss EWS 1 are marked 'Will not fix', meaning these remain permanently vulnerable in those configurations

CVSS provenance

nvdv3.13.7LOWCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
nvdv3.03.7LOWCVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
nvdv2.04.3MEDIUMAV:N/AC:M/Au:N/C:N/I:P/A:N
osv9.8CRITICAL
vendor_ubuntu9.8CRITICAL
vendor_debian3.7LOW
vendor_oracle3.7LOW
vendor_redhat3.7LOW
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