CVE-2023-0401 in OpenSSL
Summary
by MITRE • 02/08/2023
A NULL pointer can be dereferenced when signatures are being verified on PKCS7 signed or signedAndEnveloped data. In case the hash algorithm used for the signature is known to the OpenSSL library but the implementation of the hash algorithm is not available the digest initialization will fail. There is a missing check for the return value from the initialization function which later leads to invalid usage of the digest API most likely leading to a crash.
The unavailability of an algorithm can be caused by using FIPS enabled configuration of providers or more commonly by not loading the legacy provider.
PKCS7 data is processed by the SMIME library calls and also by the time stamp (TS) library calls. The TLS implementation in OpenSSL does not call these functions however third party applications would be affected if they call these functions to verify signatures on untrusted data.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 11/05/2025
The vulnerability identified as CVE-2023-0401 represents a critical NULL pointer dereference issue within the OpenSSL cryptographic library that specifically impacts the verification of PKCS7 signed and signedAndEnveloped data. This flaw occurs during the signature verification process when the system encounters a hash algorithm that is recognized by the OpenSSL library but lacks available implementation. The vulnerability stems from inadequate error handling in the digest initialization function, where the return value is not properly checked before subsequent API usage. This missing validation creates a scenario where the system attempts to dereference a NULL pointer, leading to potential application crashes and system instability.
The technical root cause of this vulnerability aligns with CWE-476, which specifically addresses NULL pointer dereference conditions in software implementations. The flaw manifests when OpenSSL's SMIME library or TS library processes PKCS7 data, particularly when dealing with cryptographic signatures that utilize hash algorithms not properly configured within the system environment. The vulnerability is particularly concerning because it can be triggered through legitimate cryptographic operations that occur during signature verification processes, making it difficult to distinguish between malicious exploitation attempts and legitimate system behavior. The issue becomes more prevalent in environments where FIPS compliance configurations are enabled or when the legacy provider is not properly loaded, as these conditions can result in algorithm unavailability even when the algorithm names are recognized by the library.
The operational impact of CVE-2023-0401 extends beyond simple application crashes to potentially enable denial of service attacks against systems that process PKCS7 signed data. While the TLS implementation within OpenSSL itself does not directly call the affected functions, third-party applications that rely on these cryptographic verification routines are at significant risk. The vulnerability affects systems processing untrusted data, making it particularly dangerous in environments where external data sources are processed without proper validation. Attackers could exploit this weakness by crafting malicious PKCS7 signed data that triggers the specific algorithm unavailability scenario, leading to system crashes that could be leveraged for service disruption. This vulnerability particularly impacts applications in the financial services, healthcare, and government sectors where PKCS7 signatures are commonly used for document authentication and timestamping.
Mitigation strategies for CVE-2023-0401 should focus on ensuring proper provider configuration and implementing robust error handling within cryptographic applications. Organizations should verify that all necessary cryptographic providers, particularly legacy providers, are properly loaded and configured in their OpenSSL environments. The recommended approach includes updating to patched versions of OpenSSL where the missing return value check has been implemented, following the principle of least privilege for cryptographic operations, and implementing proper input validation for all PKCS7 data processing. Additionally, system administrators should monitor for FIPS compliance configurations that may inadvertently disable required algorithm implementations and ensure that proper error handling mechanisms are in place to gracefully handle cryptographic algorithm unavailability conditions. The ATT&CK framework categorizes this vulnerability under T1499.004 for network denial of service and T1566.001 for spearphishing attachments, as it can be exploited through malicious signed data delivery methods. Organizations should also consider implementing intrusion detection systems that can monitor for unusual patterns of cryptographic failures that may indicate exploitation attempts.