CVE-2020-26939 : Exploit Details and Defense Strategies

In Legion of the Bouncy Castle BC before 1.61 and BC-FJA before 1.0.1.2, attackers can obtain sensitive information about a private exponent due to Observable Differences in Behavior to Error Inputs.

Understanding CVE-2020-26939

This CVE involves a vulnerability in the Bouncy Castle library that could lead to the exposure of sensitive information.

What is CVE-2020-26939?

The vulnerability allows attackers to gain insight into a private exponent by exploiting observable differences in behavior related to error inputs.

The Impact of CVE-2020-26939

The vulnerability could potentially leak information about the private exponent of an RSA private key during encryption, posing a risk to the confidentiality of encrypted data.

Technical Details of CVE-2020-26939

This section delves into the technical aspects of the vulnerability.

Vulnerability Description

The issue occurs in org.bouncycastle.crypto.encodings.OAEPEncoding, where sending invalid ciphertext that decrypts to a short payload in the OAEP Decoder may trigger an early exception, revealing information about the private exponent.

Affected Systems and Versions

Bouncy Castle BC versions before 1.61
Bouncy Castle BC-FJA versions before 1.0.1.2

Exploitation Mechanism

Attackers exploit observable differences in behavior related to error inputs to obtain sensitive information about a private exponent.

Mitigation and Prevention

Protecting systems from this vulnerability is crucial to maintaining security.

Immediate Steps to Take

Update Bouncy Castle BC and BC-FJA to versions 1.61 and 1.0.1.2, respectively.
Monitor for any unauthorized access or unusual activities that could indicate exploitation of the vulnerability.

Long-Term Security Practices

Regularly review and update cryptographic libraries to address known vulnerabilities.
Implement strong encryption practices and key management procedures to safeguard sensitive information.

Patching and Updates

Stay informed about security advisories and patches released by Bouncy Castle to address vulnerabilities like CVE-2020-26939.