OpenSSL Vulnerability: SSLv2 Version Rollback Attack in OpenSSL 1.0.2
Summary
ALPINE-CVE-2021-23839: OpenSSL 1.0.2 supports SSLv2. Affects openssl versions < 1.1.1j-r0. Fixed in 1.1.1j-r0. How to fix ↓
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Background
OpenSSL is a widely-used open-source software library that provides robust cryptographic functions and protocols for secure communication over networks. It supports various encryption algorithms and is integral to the implementation of SSL and TLS protocols. However, certain versions of OpenSSL, particularly 1.0.2, are vulnerable to a specific flaw that allows for SSLv2 version rollback attacks, compromising the security of connections.
Vulnerability Detail
The vulnerability arises from an incorrect implementation of the RSA_padding_check_SSLv23() function in OpenSSL 1.0.2, which supports SSLv2. When a client attempts to negotiate SSLv2 with a server that supports newer SSL/TLS versions, the server erroneously accepts connections if a specific padding is present, indicating a version rollback attack. This flaw can lead to unauthorized access and potential data exposure, as it allows attackers to exploit the connection by forcing a downgrade to a less secure protocol.
How To Fix
Minimum fixed version
1.1.1j-r0
This is the first release that contains the fix.
sudo apk add --upgrade opensslTip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a workaround, ensure that SSLv2 support is disabled in your OpenSSL configuration. This can be done by modifying the OpenSSL configuration file to exclude SSLv2 ciphers and protocols, thereby preventing any potential exploitation of this vulnerability.
Conclusion
The vulnerability in OpenSSL 1.0.2 related to SSLv2 version rollback attacks poses a significant risk to secure communications. Users are strongly advised to upgrade to a patched version to ensure the integrity and security of their systems. Additionally, disabling SSLv2 support can serve as an immediate mitigation strategy.
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FAQ
Only OpenSSL 1.0.2 servers from version 1.0.2s to 1.0.2x are affected. Versions 1.1.1 and later do not support SSLv2 and are not vulnerable.
A version rollback attack occurs when a client and server negotiate a connection using an older, less secure protocol version, allowing attackers to exploit vulnerabilities in that version.
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If an immediate upgrade is not possible, ensure that SSLv2 support is disabled in your configuration to mitigate the risk of exploitation.
The CVSS score for this vulnerability is 3.7, indicating a moderate level of severity.
References
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