GHSA-87mp-xc4x-x8rh: 
PHP vulnerability analysis and mitigation

The vulnerability (GHSA-87mp-xc4x-x8rh) is a Padding Oracle Vulnerability in RSA Encryption affecting the asymmetricrypt/asymmetricrypt package. This security issue was discovered in the package's encryption implementation and affects all versions up to 0.3.0. The vulnerability was initially reported on January 24, 2017, and was later addressed with a fix merged into the codebase (GitHub PR).

The vulnerability stems from improper padding implementation in RSA encryption. The package used OPENSSL_PKCS1_PADDING (PKCS v1.5) by default, which is known to be vulnerable to Bleichenbacher's attack from 1998. The vulnerability exists in the encryption and decryption processes, specifically in the openssl_private_decrypt function implementation. The issue has been classified as Moderate severity and is associated with CWE-327 (GitHub Advisory).

The vulnerability allows attackers to potentially retrieve encrypted content through a padding oracle attack. This type of attack can compromise the confidentiality of encrypted data by exploiting the system's response to different padding conditions (GitHub Issue).

The vulnerability is exploitable through Bleichenbacher's attack, a well-known padding oracle attack technique. While no specific proof of concept was publicly released, the vulnerability is similar to the one described in ZF2015-10 advisory (GitHub Issue).

The fix involves implementing OPENSSL_PKCS1_OAEP_PADDING (PKCS v2.0/OAEP) instead of the default PKCS1 v1.5 padding. This was implemented by adding the padding option set to OPENSSL_PKCS1_OAEP_PADDING in both encrypt and decrypt methods. A fix was provided through the huntr.dev platform and merged into the codebase (Huntr Fix).

The vulnerability was initially reported through GitHub Issues and later addressed through the huntr.dev bug bounty platform, where the fix was awarded $25. The security community acknowledged the importance of proper padding in RSA encryption implementations (GitHub PR).