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OpenSSL: Incorrect SSLv2 rollback protection (CVE-2021-23839) (Linux)
Information
Severity
Severity
Family
Family
CVSSv2 Base
CVSSv2 Base
CVSSv2 Vector
CVSSv2 Vector
Solution Type
Solution Type
Created
Created
Modified
Modified
Summary
OpenSSL is prone to an incorrect SSLv2 rollback protection vulnerability.
Insight
Insight
OpenSSL 1.0.2 supports SSLv2. If a client attempts to negotiate SSLv2 with a server that is configured to support both SSLv2 and more recent SSL and TLS versions then a check is made for a version rollback attack when unpadding an RSA signature. Clients that support SSL or TLS versions greater than SSLv2 are supposed to use a special form of padding. A server that supports greater than SSLv2 is supposed to reject connection attempts from a client where this special form of padding is present, because this indicates that a version rollback has occurred (i.e. both client and server support greater than SSLv2, and yet this is the version that is being requested). The implementation of this padding check inverted the logic so that the connection attempt is accepted if the padding is present, and rejected if it is absent. This means that such as server will accept a connection if a version rollback attack has occurred. Further the server will erroneously reject a connection if a normal SSLv2 connection attempt is made.
Affected Software
Affected Software
OpenSSL versions 1.0.2s - 1.0.2x.
Detection Method
Detection Method
Checks if a vulnerable version is present on the target host.
Solution
Solution
Update OpenSSL to version 1.0.2y, 1.1.1j or later. See the references for more details.