CVE-2021-23839

Publication date 16 February 2021

Last updated 24 July 2024

Ubuntu priority

Low

Why this priority?

Cvss 3 Severity Score

3.7 · Low

Score breakdown

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. Only OpenSSL 1.0.2 servers from version 1.0.2s to 1.0.2x are affected by this issue. In order to be vulnerable a 1.0.2 server must: 1) have configured SSLv2 support at compile time (this is off by default), 2) have configured SSLv2 support at runtime (this is off by default), 3) have configured SSLv2 ciphersuites (these are not in the default ciphersuite list) OpenSSL 1.1.1 does not have SSLv2 support and therefore is not vulnerable to this issue. The underlying error is in the implementation of the RSA_padding_check_SSLv23() function. This also affects the RSA_SSLV23_PADDING padding mode used by various other functions. Although 1.1.1 does not support SSLv2 the RSA_padding_check_SSLv23() function still exists, as does the RSA_SSLV23_PADDING padding mode. Applications that directly call that function or use that padding mode will encounter this issue. However since there is no support for the SSLv2 protocol in 1.1.1 this is considered a bug and not a security issue in that version. OpenSSL 1.0.2 is out of support and no longer receiving public updates. Premium support customers of OpenSSL 1.0.2 should upgrade to 1.0.2y. Other users should upgrade to 1.1.1j. Fixed in OpenSSL 1.0.2y (Affected 1.0.2s-1.0.2x).

Read the notes from the security team

Status

Package Ubuntu Release Status
edk2 21.04 hirsute
Not affected
20.10 groovy
Not affected
20.04 LTS focal
Not affected
18.04 LTS bionic
Not affected
16.04 LTS xenial
Not affected
14.04 LTS trusty Not in release
nodejs 21.04 hirsute
Not affected
20.10 groovy
Not affected
20.04 LTS focal
Not affected
18.04 LTS bionic
Not affected
16.04 LTS xenial
Not affected
14.04 LTS trusty
Not affected
openssl 21.04 hirsute
Not affected
20.10 groovy
Not affected
20.04 LTS focal
Not affected
18.04 LTS bionic
Not affected
16.04 LTS xenial
Not affected
14.04 LTS trusty
Not affected
openssl1.0 21.04 hirsute Not in release
20.10 groovy Not in release
20.04 LTS focal Not in release
18.04 LTS bionic
Not affected
16.04 LTS xenial Not in release
14.04 LTS trusty Not in release

Notes

avital

openssl in Ubuntu is compiled with no-ssl2

Severity score breakdown

Parameter Value
Base score 3.7 · Low
Attack vector Network
Attack complexity High
Privileges required None
User interaction None
Scope Unchanged
Confidentiality None
Integrity impact Low
Availability impact None
Vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N