CVE-2022-4304: Timing-Based Side Channel Attack in OpenSSL RSA Decryption Implementation

A critical vulnerability, CVE-2022-4304, has been identified in the OpenSSL RSA decryption implementation. This vulnerability is a timing-based side channel attack, which, if exploited, could potentially allow an attacker to recover plaintext across a network in a Bleichenbacher style attack. This post will provide details on the exploit, code snippets, and links to original references.

Exploit Details

This attack targets OpenSSL's implementation of RSA decryption, affecting all RSA padding modes, including PKCS#1 v1.5, RSA-OEAP, and RSASVE. In a TLS connection, for example, RSA is commonly employed by a client to send an encrypted pre-master secret to a server. An attacker who has observed an authentic connection between a client and a server could use this vulnerability to send a large number of trial messages for decryption to the server and record the time taken to process them. Eventually, after processing enough messages, the attacker could recover the original pre-master secret used for the connection and subsequently decrypt the application data sent over that connection.

Code Snippet

The following code snippet demonstrates the potential exploit, where 'send_trial_message()' represents the attacker sending a trial message and 'timing' records the time taken to process the message.

pre_master_secret = None
timing_data = []
trial_messages = generate_trial_messages()

for message in trial_messages:
    start_time = time.time()
    response = send_trial_message(message)
    elapsed_time = time.time() - start_time
    timing_data.append((message, elapsed_time))

pre_master_secret = recover_pre_master_secret(timing_data)

Original References

1. CVE-2022-4304 - Public Vulnerability Announcement
2. OpenSSL Security Advisory
3. Bleichenbacher's RSA Attack

Mitigation

Users are advised to update their OpenSSL installations to the latest version to protect against this vulnerability. Additionally, maintainers of applications and libraries that rely on OpenSSL's RSA implementation should ensure that they are using a patched version and update their software accordingly.

Conclusion

CVE-2022-4304 is a critical timing-based side channel vulnerability in OpenSSL's RSA decryption implementation. Attackers can potentially exploit this flaw to recover plaintext across a network by sending a large number of trial messages to a target server and recording the processing times. To mitigate this vulnerability, users should update their OpenSSL installations and application maintainers should ensure their software is using patched OpenSSL versions.

Timeline

Published on: 02/08/2023 20:15:00 UTC
Last modified on: 02/24/2023 17:13:00 UTC