CVE-2023-33850: IBM TXSeries Information Disclosure Flaw

CVE-2023-33850 Overview

IBM GSKit-Crypto contains a timing-based side channel vulnerability in its RSA Decryption implementation that could allow a remote attacker to obtain sensitive information. By sending an overly large number of trial messages for decryption, an attacker could exploit this vulnerability to extract cryptographic secrets through careful timing analysis of the decryption operations.

This vulnerability is classified as CWE-203 (Observable Discrepancy), which occurs when a product behaves differently or sends different responses in ways that can be observed by unauthorized actors, revealing sensitive information about the system's internal state.

Critical Impact

Remote attackers can exploit timing differences in RSA decryption to extract sensitive cryptographic material without authentication, potentially compromising encrypted communications across multiple IBM enterprise products.

Affected Products

• IBM TXSeries for Multiplatform 8.1, 8.2, and 9.1
• IBM CICS TX 10.1 (Advanced) and 11.1 (Standard/Advanced)
• Systems running on IBM AIX, Linux, HP-UX, and Microsoft Windows

Discovery Timeline

• 2023-08-22 - CVE-2023-33850 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2023-33850

Vulnerability Analysis

The vulnerability resides in the IBM GSKit-Crypto library's RSA decryption implementation. The cryptographic implementation exhibits observable timing variations when processing decryption operations, creating a side channel that attackers can exploit. This type of vulnerability falls under timing attacks, a subset of side channel attacks that infer secret information by measuring the time taken to execute cryptographic algorithms.

The attack requires the adversary to send a large number of specially crafted trial messages for decryption while precisely measuring the response times. Through statistical analysis of these timing measurements, an attacker can gradually recover the RSA private key or decrypt previously captured ciphertext. The network-based attack vector means exploitation can occur remotely without any privileges or user interaction required.

The impact is limited to confidentiality compromise, as the vulnerability allows information disclosure but does not enable modification of data or denial of service conditions.

Root Cause

The root cause is non-constant-time execution in the RSA decryption implementation within IBM GSKit-Crypto. Cryptographic operations that process secret data must execute in constant time regardless of the input values to prevent timing-based information leakage. The GSKit-Crypto library fails to maintain this property, resulting in measurable timing variations that correlate with the secret key material being processed.

This is a well-known class of cryptographic implementation weakness that has affected numerous RSA implementations historically. Modern cryptographic best practices mandate constant-time implementations for all operations involving secret data, including RSA decryption, signature generation, and key operations.

Attack Vector

The attack can be conducted remotely over the network by any unauthenticated attacker who can send encrypted messages to a vulnerable service and measure response times. The exploitation methodology involves:

1. Establishing a connection to the target service that uses GSKit-Crypto for TLS or other cryptographic operations
2. Sending a large volume of carefully crafted ciphertext messages designed to trigger measurable timing variations
3. Recording precise timing measurements for each decryption operation
4. Applying statistical analysis techniques to correlate timing differences with intermediate computation values
5. Gradually recovering the private key material or decrypting specific ciphertext

The attack complexity is relatively low from a technical standpoint, though it requires the ability to send many trial messages and collect accurate timing measurements. Network jitter can complicate remote timing attacks but does not eliminate the vulnerability. For more technical details, refer to the IBM X-Force Vulnerability #257132.

Detection Methods for CVE-2023-33850

Indicators of Compromise

• Unusual volume of TLS handshake attempts or encrypted message submissions to services using GSKit-Crypto
• Statistical anomalies in connection patterns suggesting timing measurement collection
• High-frequency connection/disconnection cycles from single source IPs targeting cryptographic endpoints
• Network traffic patterns consistent with oracle-based cryptographic attacks

Detection Strategies

• Monitor for abnormally high volumes of failed or repeated cryptographic operations from single sources
• Implement rate limiting on TLS handshakes and encrypted message processing to impede timing attack data collection
• Deploy network intrusion detection signatures for known timing attack patterns
• Audit GSKit-Crypto library versions across the environment to identify vulnerable deployments

Monitoring Recommendations

• Enable detailed logging on all services utilizing GSKit-Crypto for cryptographic operations
• Monitor connection frequency and timing patterns to cryptographic endpoints
• Establish baseline metrics for normal cryptographic operation volumes to detect anomalous activity
• Configure SentinelOne Singularity Platform to alert on suspicious patterns targeting vulnerable IBM products

How to Mitigate CVE-2023-33850

Immediate Actions Required

• Inventory all deployments of IBM TXSeries for Multiplatform and CICS TX to identify vulnerable systems
• Prioritize patching internet-facing services and systems handling sensitive encrypted data
• Review network exposure and consider implementing additional rate limiting on affected services
• Apply vendor patches from IBM as soon as possible

Patch Information

IBM has released security updates to address this vulnerability. Administrators should apply the appropriate fixes based on their deployed products:

• For IBM TXSeries for Multiplatform: See IBM Support Document #7010369
• For IBM CICS TX: See IBM Support Document #7022413 and IBM Support Document #7022414

Additionally, NetApp Security Advisory NTAP-20241108-0002 provides guidance for affected NetApp products.

Workarounds

• Implement network-level rate limiting to reduce the volume of trial messages an attacker can send
• Deploy web application firewalls or network security appliances to detect and block timing attack patterns
• Consider placing vulnerable services behind VPN or other access controls to limit attacker exposure
• Monitor for unusual traffic patterns while awaiting patch deployment

# Example: Configure rate limiting on Linux using iptables
# Limit new connections to 10 per minute per source IP
iptables -A INPUT -p tcp --dport 443 -m state --state NEW -m recent --set
iptables -A INPUT -p tcp --dport 443 -m state --state NEW -m recent --update --seconds 60 --hitcount 10 -j DROP