The OpenSSL public API function X509_issuer_and_serial_hash() attempts to create a unique hash value based on the issuer and serial number data contained within an X509 certificate. However, it fails to correctly handle any errors that may occur while parsing the issuer field, which might occur if the issuer field is maliciously constructed. This may subsequently result in a NULL pointer dereference and a crash leading to a potential denial of service attack. The function X509_issuer_and_serial_hash() is never directly called by OpenSSL itself, so applications are only vulnerable if they use this function directly and on certificates that may have been obtained from untrusted sources.
OpenSSL versions 1.1.1i and below are affected by this issue. Users of these versions should upgrade to OpenSSL 1.1.1j. OpenSSL versions 1.0.2x and below are affected by this issue, but OpenSSL 1.0.2 is out of support and no longer receiving public updates. Premium support customers of OpenSSL 1.0.2 should upgrade to 1.0.2y. Other users should upgrade to 1.1.1j. This vulnerability allows for potential denial of service.
Risk to organizations includes service disruptions, which can be critical for services relying on OpenSSL for secure communications. Organizations should prioritize patching immediately.
The vulnerability is classified as medium severity due to its CVSS score of 5.9. Given the potential for denial of service, it is recommended for organizations using vulnerable versions of OpenSSL to take immediate action.
Vulnerability Details
The OpenSSL public API function X509_issuer_and_serial_hash() attempts to create a unique hash value based on the issuer and serial number data contained within an X509 certificate. However, it fails to correctly handle any errors that may occur while parsing the issuer field. This can lead to a NULL pointer dereference, resulting in a crash.
OpenSSL versions 1.1.1i and below are affected by this vulnerability. Users should upgrade to OpenSSL 1.1.1j. For OpenSSL versions 1.0.2x and below, users should upgrade to 1.0.2y if they are premium support customers, or to 1.1.1j otherwise.
Technical Analysis
The root cause of this vulnerability is improper error handling in the X509_issuer_and_serial_hash() function. If a maliciously crafted issuer field is parsed, it may lead to a NULL pointer dereference. The attack vector is network-based, and the complexity is high, as it requires an attacker to have control over the certificate being parsed. No privileges are required for exploitation, and user interaction is not necessary.
The confidentiality and integrity impacts are none, but there is a high impact on availability due to the potential denial of service. This indicates that while the attacker cannot access sensitive data or modify it, they can disrupt services.
Risk & Impact Analysis
Organizations utilizing OpenSSL in their applications must assess the risk of this vulnerability. The denial of service potential can disrupt critical services, affecting business operations. The blast radius is significant, especially for organizations relying on secure communications. The urgency for remediation is medium; organizations should schedule remediation as part of their priority patch cycle.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | Yes |
Public PoC | Yes |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
OpenSSL versions 1.1.1i and below, as well as 1.0.2x and below, are affected by this vulnerability. Users should upgrade to OpenSSL 1.1.1j or 1.0.2y depending on their current version.
Mitigation & Remediation
Organizations are advised to patch their installations of OpenSSL. Upgrade to OpenSSL 1.1.1j for versions 1.1.1i and below. For 1.0.2x and below, upgrade to 1.0.2y if premium support is available, otherwise upgrade to 1.1.1j.
If an immediate upgrade is not possible, organizations should implement network controls to restrict untrusted certificates and monitor for anomalous behavior related to certificate handling.
For further information on security testing, organizations may consider penetration testing to assess their current security posture.
Detection Guidance
Organizations should monitor logs for unusual certificate parsing errors and behavior indicative of denial of service attempts. Behavioral anomalies when handling certificates from untrusted sources should also be investigated.
AppSecure Threat Intelligence Insight
The long-term significance of this vulnerability is its reflection of the need for robust error handling in security libraries. It highlights a pattern where improper validation can lead to significant availability impacts.
Security teams should take this opportunity to review their application security practices, ensuring that all external inputs, particularly from certificates, are rigorously validated.
For more insights on security practices, consider reviewing our articles on penetration testing methodology and vulnerability management programs to strengthen your defenses.
Additionally, embracing a proactive approach through cloud security assessments can further mitigate risks associated with vulnerabilities like CVE-2021-23841.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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