Vulnerability Details

OpenSSL: Incorrect SSLv2 rollback protection (CVE-2021-23839) (Linux)

Published: 2021-02-17 05:49:06
CVE Author: NIST National Vulnerability Database

CVSS Base Vector:
AV:N/AC:L/Au:N/C:N/I:N/A:P

Detection Type:
Remote Banner Unreliable

Solution Type:
Vendor Patch

Summary:
OpenSSL is prone to an incorrect SSLv2 rollback protection vulnerability.

Detection Method:
Checks if a vulnerable version is present on the target host.

Technical Details:
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 Versions:
OpenSSL versions 1.0.2s - 1.0.2x.

Recommendations:
Update OpenSSL to version 1.0.2y, 1.1.1j or later. See the references for more details.

NIST (National Institute of Standards and Technology) NVD (National Vulnerability Database)

https://nvd.nist.gov/vuln/detail/CVE-2021-23839

References:

https://www.openssl.org/news/secadv/20210216.txt

Severity
Medium
CVSS Score
5.0
Published
2021-02-17
Modified
2021-02-17
Category
Denial of Service

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