CVE-2024-2236: libgcrypt RSA Information Disclosure Flaw

CVE-2024-2236 Overview

A timing-based side-channel vulnerability has been identified in libgcrypt's RSA implementation. This flaw enables remote attackers to potentially initiate a Bleichenbacher-style attack, which can lead to the decryption of RSA ciphertexts. The vulnerability exists due to observable timing differences during RSA decryption operations, allowing attackers to deduce information about the plaintext through careful measurement and statistical analysis.

Critical Impact

Successful exploitation could allow remote attackers to decrypt RSA-encrypted communications without possessing the private key, compromising the confidentiality of sensitive data protected by affected libgcrypt implementations.

Affected Products

• libgcrypt (RSA implementation)
• Red Hat Enterprise Linux distributions using vulnerable libgcrypt versions
• Systems and applications depending on libgcrypt for cryptographic operations

Discovery Timeline

• 2024-03-06 - CVE-2024-2236 published to NVD
• 2025-04-02 - Last updated in NVD database

Technical Details for CVE-2024-2236

Vulnerability Analysis

This vulnerability is classified under CWE-208 (Observable Timing Discrepancy), which occurs when two separate code paths in an application take different amounts of time to execute, potentially leaking information about which path was taken. In the context of libgcrypt's RSA implementation, the timing differences during decryption operations can be exploited to perform a Bleichenbacher-style attack.

The Bleichenbacher attack, originally discovered in 1998, exploits implementations of PKCS#1 v1.5 RSA encryption that provide different responses (including timing variations) when processing malformed ciphertexts. By submitting carefully crafted ciphertexts and observing the timing of responses, an attacker can gradually recover the plaintext without access to the private key.

The network-based attack vector combined with no required privileges or user interaction makes this vulnerability exploitable by remote attackers who can observe timing differences in RSA operations. While the attack complexity is high due to the need for precise timing measurements and statistical analysis, successful exploitation results in a complete compromise of confidentiality for RSA-encrypted data.

Root Cause

The root cause of this vulnerability lies in the non-constant-time implementation of RSA decryption operations in libgcrypt. When processing RSA ciphertexts, the code exhibits measurable timing variations based on the input data and intermediate calculation results. These timing side-channels allow attackers to infer information about the private key or plaintext through statistical analysis of multiple decryption operations.

Constant-time implementations are essential for cryptographic operations to prevent timing-based side-channel attacks. When cryptographic code branches or performs operations that take variable time depending on secret data, attackers can exploit these timing differences to extract sensitive information.

Attack Vector

The attack requires network access to a service performing RSA decryption with the vulnerable libgcrypt implementation. An attacker would:

1. Send numerous carefully crafted ciphertexts to the target service
2. Measure the response times for each decryption operation with high precision
3. Apply statistical analysis to correlate timing variations with ciphertext properties
4. Gradually deduce the plaintext or private key information through iterative refinement

The Bleichenbacher attack methodology leverages the padding oracle behavior where timing differences reveal whether a decrypted ciphertext has valid PKCS#1 v1.5 padding. This information, combined with the mathematical properties of RSA, allows the attacker to systematically recover the original plaintext.

Detection Methods for CVE-2024-2236

Indicators of Compromise

• Unusual volumes of failed or malformed RSA decryption attempts from single source IPs
• Statistically abnormal patterns of cryptographic API calls targeting RSA operations
• Network traffic analysis revealing timing probe patterns consistent with Bleichenbacher attacks
• Log entries showing repeated RSA operation errors with varying ciphertext inputs

Detection Strategies

• Monitor cryptographic operation logs for anomalous patterns of RSA decryption requests
• Implement network traffic analysis to detect timing probe attacks
• Deploy intrusion detection rules that flag high-volume decryption requests from individual sources
• Use application-level monitoring to track RSA operation performance metrics and identify probing activity

Monitoring Recommendations

• Enable detailed logging for applications using libgcrypt RSA functionality
• Implement rate limiting on services performing RSA decryption operations
• Configure alerting for unusual spikes in cryptographic operation failures
• Deploy network-based anomaly detection focused on TLS/SSL handshake patterns

How to Mitigate CVE-2024-2236

Immediate Actions Required

• Update libgcrypt to the latest patched version available for your distribution
• Review and update all systems and applications that depend on libgcrypt for RSA operations
• Consider temporarily disabling RSA-based functionality in critical applications until patches are applied
• Implement network-level controls to limit exposure of vulnerable services

Patch Information

Red Hat has released security advisories addressing this vulnerability. Organizations using Red Hat Enterprise Linux should apply the following patches:

• Red Hat Security Advisory RHSA-2024:9404
• Red Hat Security Advisory RHSA-2025:3530
• Red Hat Security Advisory RHSA-2025:3534

Additional technical details are available via Red Hat CVE Analysis CVE-2024-2236 and related bug reports #2245218 and #2268268.

Workarounds

• Implement additional network-level access controls to limit exposure of services using RSA decryption
• Consider transitioning to OAEP (Optimal Asymmetric Encryption Padding) instead of PKCS#1 v1.5 where possible
• Deploy rate limiting on cryptographic endpoints to make timing attacks more difficult
• Use application-level firewalls to detect and block patterns consistent with Bleichenbacher attack probing

# Check current libgcrypt version on Red Hat-based systems
rpm -q libgcrypt

# Update libgcrypt to patched version
sudo dnf update libgcrypt

# Verify update was applied
rpm -q libgcrypt