Log4j-core-2.6.1.jar Vulnerabilities: A Detailed Analysis

Nov 24, 2025 by Alex Johnson 58 views

In this article, we delve into the vulnerabilities discovered in the log4j-core-2.6.1.jar library. This library, an integral part of the Apache Log4j implementation, has been found to contain multiple security flaws. Understanding these vulnerabilities is crucial for developers and system administrators to secure their applications and systems effectively. We will explore each vulnerability in detail, providing insights into their potential impact and available remediation.

Understanding the Vulnerabilities in Log4j-core-2.6.1.jar

The log4j-core-2.6.1.jar library, a component of the widely-used Apache Log4j logging framework, is susceptible to several security vulnerabilities. These vulnerabilities, if exploited, can lead to significant risks, including remote code execution, information disclosure, and denial of service. In this comprehensive analysis, we will dissect each vulnerability, providing a clear understanding of the threats they pose and the steps needed to mitigate them. Our aim is to equip you with the knowledge necessary to protect your systems and applications from potential attacks targeting these weaknesses in log4j-core-2.6.1.jar. We will cover the specific CVEs associated with these vulnerabilities, their severity levels, and the recommended upgrade paths to secure versions.

CVE-2021-44228: Critical Remote Code Execution Vulnerability

The most critical vulnerability, CVE-2021-44228, also known as “Log4Shell,” carries a severity score of 10.0. This vulnerability arises from the JNDI (Java Naming and Directory Interface) features used in Log4j 2.0-beta9 through 2.15.0. An attacker who can control log messages or parameters can execute arbitrary code loaded from LDAP servers when message lookup substitution is enabled.

Impact of CVE-2021-44228

The impact of CVE-2021-44228 is severe. It allows for remote code execution, meaning an attacker can gain complete control over the affected system. This can lead to data breaches, system downtime, and other malicious activities. The high exploit maturity and EPSS score of 94.5% indicate that this vulnerability is actively exploited in the wild, making it a significant threat.

Remediation for CVE-2021-44228

To mitigate CVE-2021-44228, it is recommended to upgrade to Log4j versions 2.3.1, 2.12.2, or 2.15.0. These versions disable JNDI lookup by default or completely remove the vulnerable functionality. If upgrading is not immediately feasible, consider implementing workarounds such as setting the log4j2.formatMsgNoLookups system property to true.

CVE-2017-5645: Critical Deserialization Vulnerability

Another critical vulnerability, CVE-2017-5645, has a severity score of 9.8. This vulnerability occurs when using the TCP socket server or UDP socket server to receive serialized log events. A specially crafted binary payload can be sent that, when deserialized, can execute arbitrary code. This vulnerability highlights the dangers of insecure deserialization in logging frameworks.

Impact of CVE-2017-5645

The impact of CVE-2017-5645 is also critical, as it allows for arbitrary code execution. An attacker can send a malicious payload to the Log4j server, leading to system compromise. The high EPSS score of 94.0% underscores the potential for exploitation.

Remediation for CVE-2017-5645

To address CVE-2017-5645, it is essential to upgrade to Log4j version 2.8.2 or later. This version includes a fix that prevents the deserialization of untrusted data, effectively mitigating the vulnerability.

CVE-2021-45046: Critical Information Leak and Remote Code Execution

CVE-2021-45046, with a severity score of 9.0, is a critical vulnerability that stems from an incomplete fix for CVE-2021-44228. In certain non-default configurations, attackers with control over Thread Context Map (MDC) input data can craft malicious input data using a JNDI Lookup pattern, leading to information leakage and remote code execution. This vulnerability underscores the complexity of patching security flaws and the importance of thorough fixes.

Impact of CVE-2021-45046

The impact of CVE-2021-45046 is significant, potentially leading to both information leakage and remote code execution. Attackers can exploit this vulnerability to gain unauthorized access to sensitive data or execute malicious code on the affected system. The high exploit maturity and EPSS score of 94.3% highlight the urgency of addressing this vulnerability.

Remediation for CVE-2021-45046

To resolve CVE-2021-45046, upgrade to Log4j versions 2.3.1, 2.12.2, or 2.16.0. These versions remove support for message lookup patterns and disable JNDI functionality by default, effectively preventing exploitation.

CVE-2021-44832: Medium Severity Remote Code Execution

CVE-2021-44832, a medium severity vulnerability with a score of 6.6, allows for remote code execution when a configuration uses a JDBC Appender with a JNDI LDAP data source URI. This vulnerability can be exploited if an attacker has control of the target LDAP server. This highlights the importance of securing not just the Log4j library itself, but also the configurations and dependencies used in conjunction with it.

Impact of CVE-2021-44832

The impact of CVE-2021-44832 is substantial, as it can lead to remote code execution. An attacker who controls the LDAP server can leverage this vulnerability to compromise the system. The exploit maturity is high, and the EPSS score is 55.5%, indicating a moderate level of risk.

Remediation for CVE-2021-44832

To address CVE-2021-44832, upgrade to Log4j versions 2.3.2, 2.12.4, or 2.17.1. These versions limit JNDI data source names to the java protocol, preventing exploitation via LDAP.

CVE-2021-45105: Medium Severity Denial of Service

CVE-2021-45105, with a severity score of 5.9, is a medium severity vulnerability that can lead to a denial of service. This vulnerability occurs due to uncontrolled recursion from self-referential lookups. An attacker with control over Thread Context Map data can cause a denial of service when a crafted string is interpreted. This type of vulnerability can disrupt services and impact system availability.

Impact of CVE-2021-45105

The primary impact of CVE-2021-45105 is a denial of service. By exploiting this vulnerability, an attacker can make the system unresponsive, preventing legitimate users from accessing services. The high exploit maturity and EPSS score of 66.7% indicate a significant risk of exploitation.

Remediation for CVE-2021-45105

To mitigate CVE-2021-45105, upgrade to Log4j versions 2.3.1, 2.12.3, or 2.17.0. These versions protect against uncontrolled recursion from self-referential lookups, resolving the denial of service issue.

CVE-2020-9488: Low Severity Man-in-the-Middle Attack

CVE-2020-9488, a low severity vulnerability with a score of 3.7, involves improper validation of certificates with host mismatch in the Apache Log4j SMTP appender. This could allow an SMTPS connection to be intercepted by a man-in-the-middle attack, potentially leaking log messages sent through that appender. While the severity is low, the potential for information leakage should not be ignored.

Impact of CVE-2020-9488

The impact of CVE-2020-9488 is primarily the potential for a man-in-the-middle attack. This can lead to the disclosure of sensitive information contained in log messages. The low EPSS score (less than 1%) suggests a low likelihood of exploitation, but the risk remains.

Remediation for CVE-2020-9488

To address CVE-2020-9488, upgrade to ch.qos.reload4j:reload4j version 1.2.18.3. This version includes a fix for the certificate validation issue, preventing man-in-the-middle attacks.

Comprehensive Remediation Strategies for Log4j Vulnerabilities

Addressing vulnerabilities in log4j-core-2.6.1.jar requires a multifaceted approach. The primary strategy is to upgrade to the latest secure version of Log4j. However, in cases where immediate upgrades are not feasible, implementing temporary workarounds and mitigation techniques is crucial. These may include disabling vulnerable features, applying security patches, and implementing network-level controls to restrict potential attack vectors. Continuous monitoring and regular security assessments are also vital to ensure ongoing protection against emerging threats. A comprehensive remediation plan should encompass both immediate actions and long-term strategies to maintain the security and integrity of systems using Log4j. By staying vigilant and proactive, organizations can minimize their risk exposure and safeguard their critical assets from exploitation.

Conclusion

The vulnerabilities in log4j-core-2.6.1.jar pose significant risks to applications and systems. Understanding these vulnerabilities and implementing the recommended remediations is crucial for maintaining security. By upgrading to the latest secure versions and applying appropriate mitigation measures, developers and system administrators can protect their environments from potential attacks. Remember, security is an ongoing process, and staying informed about new vulnerabilities and best practices is essential.

For more information on Log4j vulnerabilities and security best practices, visit the Apache Log4j Security Vulnerabilities page.