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Mozilla Foundation Security Advisory 2015-150

MD5 signatures accepted within TLS 1.2 ServerKeyExchange in server signature

December 22, 2015
Karthikeyan Bhargavan
Firefox, Firefox ESR, Thunderbird
Fixed in
  • Firefox 43.0.2
  • Firefox ESR 38.6
  • Thunderbird 38.6


Security researcher Karthikeyan Bhargavan reported an issue in Network Security Services (NSS) where MD5 signatures in the server signature within the TLS 1.2 ServerKeyExchange message are still accepted. This is an issue since NSS has officially disallowed the accepting MD5 as a hash algorithm in signatures since 2011. This issues exposes NSS based clients such as Firefox to theoretical collision-based forgery attacks. This issue was fixed in NSS version 3.20.2.