CVE-2023-0286: OpenSSL Type Confusion DoS Vulnerability

CVE-2023-0286 Overview

CVE-2023-0286 is a type confusion vulnerability in OpenSSL affecting X.400 address processing within X.509 GeneralName structures. The vulnerability stems from X.400 addresses being parsed as ASN1_STRING while the public structure definition for GENERAL_NAME incorrectly specifies the type of the x400Address field as ASN1_TYPE. This field is subsequently interpreted by the OpenSSL function GENERAL_NAME_cmp as an ASN1_TYPE rather than an ASN1_STRING, leading to potential memory disclosure or denial of service conditions.

When CRL checking is enabled (specifically when an application sets the X509_V_FLAG_CRL_CHECK flag), this vulnerability may allow an attacker to pass arbitrary pointers to a memcmp call, enabling them to read memory contents or cause a denial of service.

Critical Impact

Type confusion vulnerability enables attackers to read sensitive memory contents or cause denial of service when CRL checking is enabled in OpenSSL-based applications.

Affected Products

• OpenSSL (multiple versions)
• Stormshield Management Center
• Stormshield Network Security

Discovery Timeline

• 2023-02-07 - OpenSSL releases security advisory
• 2023-02-08 - CVE-2023-0286 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2023-0286

Vulnerability Analysis

This type confusion vulnerability occurs during the processing of X.509 certificates containing X.400 addresses. The root issue lies in a mismatch between how X.400 addresses are parsed internally versus how they are defined in the public API structures. When GENERAL_NAME_cmp processes these structures, it incorrectly interprets the memory layout, potentially allowing memory disclosure or crash conditions.

The attack scenario requires CRL (Certificate Revocation List) checking to be enabled in the target application. In most cases, the attacker needs to provide both the certificate chain and CRL, neither of which requires a valid signature. If the attacker controls only one of these inputs, the other must already contain an X.400 address as a CRL distribution point, which is uncommon in practice.

This vulnerability primarily affects applications that have implemented custom functionality for retrieving CRLs over a network, as these are more likely to process attacker-controlled certificate data with CRL validation enabled.

Root Cause

The vulnerability originates from an inconsistency in the OpenSSL codebase where the x400Address field within the GENERAL_NAME structure is defined as ASN1_TYPE in the public headers, but X.400 addresses are actually parsed and stored as ASN1_STRING internally. When the GENERAL_NAME_cmp function performs comparisons, it treats the field according to the public definition (ASN1_TYPE), leading to type confusion when processing actual X.400 address data stored as ASN1_STRING.

Attack Vector

The attack vector is network-based and requires the following conditions:

1. The target application must have CRL checking enabled via the X509_V_FLAG_CRL_CHECK flag
2. The attacker must be able to supply either a malicious certificate chain, a malicious CRL, or both
3. The malicious data must contain specially crafted X.400 address fields

In the optimal attack scenario, the attacker provides both the certificate chain and CRL with crafted X.400 addresses. This causes the GENERAL_NAME_cmp function to interpret the ASN1_STRING data as ASN1_TYPE, potentially leading to arbitrary pointer dereference during the memcmp operation. This can result in reading out-of-bounds memory or causing application crashes.

Detection Methods for CVE-2023-0286

Indicators of Compromise

• Unexpected application crashes in services using OpenSSL for certificate validation
• Anomalous memory access patterns or segmentation faults in TLS-enabled applications
• CRL processing errors or unexpected behavior during certificate chain validation
• Memory disclosure symptoms such as sensitive data appearing in network responses

Detection Strategies

• Monitor application logs for crashes related to X.509 certificate processing or CRL validation
• Implement network traffic analysis to detect malformed certificates or CRLs being sent to vulnerable services
• Deploy endpoint detection to identify exploitation attempts targeting OpenSSL-based applications
• Use vulnerability scanners to identify systems running affected OpenSSL versions

Monitoring Recommendations

• Enable detailed logging for certificate validation operations in critical applications
• Monitor memory usage patterns in services performing CRL checking operations
• Set up alerts for repeated certificate validation failures or crashes in TLS-enabled services
• Track OpenSSL version information across infrastructure to identify vulnerable deployments

How to Mitigate CVE-2023-0286

Immediate Actions Required

• Upgrade OpenSSL to a patched version immediately on all affected systems
• If upgrading is not immediately possible, consider disabling CRL checking as a temporary measure
• Review applications that implement custom CRL retrieval functionality for exposure to this vulnerability
• Audit systems to identify all OpenSSL deployments and prioritize patching based on exposure

Patch Information

OpenSSL has released patches addressing this vulnerability. The fixes are available through the official OpenSSL repository:

• OpenSSL Commit Diff 2c6c9d4
• OpenSSL Commit Diff 2f75300
• OpenSSL Commit Diff fd2af07

For complete details, refer to the OpenSSL Security Advisory 2023-02-07. LibreSSL users should update to version 3.6.2 or later per the OpenBSD LibreSSL Release Notes.

Workarounds

• Disable CRL checking by not setting the X509_V_FLAG_CRL_CHECK flag if certificate revocation checking can be temporarily disabled
• Implement strict input validation for certificates and CRLs before processing them with OpenSSL
• Restrict network sources from which certificates and CRLs are accepted to trusted origins only
• Consider using OCSP (Online Certificate Status Protocol) as an alternative to CRL checking until patching is complete

# Check OpenSSL version to determine if patching is required
openssl version -a

# Verify the installed OpenSSL library version
dpkg -l | grep openssl  # Debian/Ubuntu
rpm -qa | grep openssl  # RHEL/CentOS