GnuPG 1.4.x, 2.0.x, and 2.1.x treats a key flags subpacket with all
bits cleared (no usage permitted) as if it has all bits set (all usage
permitted), which might allow remote attackers to bypass intended
cryptographic protection mechanisms by leveraging the subkey.
Note:References are provided for the convenience of the reader to help distinguish between vulnerabilities. The list is not intended to be complete.
MLIST:[oss-security] 20130913 Re: GnuPG treats no-usage-permitted keys as all-usages-permitted
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