CVE-2021-27905 is a critical SSRF vulnerability affecting Apache Solr, specifically in the ReplicationHandler component, which is registered at "/replication". The vulnerability arises from the absence of proper validation for the "masterUrl" parameter, which designates another ReplicationHandler on a different Solr core to replicate index data. This oversight allows attackers to send crafted requests that could exploit the system, leading to unauthorized access to internal services. With a CVSS score of 9.8, this vulnerability poses a significant risk to organizations utilizing affected versions of Apache Solr.
The vulnerability was first published on April 13, 2021, and affects all versions of Apache Solr prior to 8.8.2. The failure to validate the "masterUrl" against configurations used for the "shards" parameter has created a critical security gap. This vulnerability allows for potential exploitation that can affect the confidentiality, integrity, and availability of the system, making it crucial for organizations to address this issue promptly.
Organizations should prioritize patching immediately to mitigate the risks associated with this vulnerability. The fix was introduced in version 8.8.2, and it is essential for users to upgrade to this version or later to ensure their systems are secure against potential exploitation.
The risk to organizations includes unauthorized access to sensitive internal services and data, which could lead to further attacks or data breaches. Given the critical nature of this vulnerability and its high CVSS score, organizations using Apache Solr must act swiftly to protect their systems.
Vulnerability Details
The official description of CVE-2021-27905 states that the ReplicationHandler in Apache Solr has a "masterUrl" parameter that lacks validation against the "shards" parameter configuration. This issue has been classified under CWE-918, indicating a Server-Side Request Forgery vulnerability. The vulnerability affects all versions of Solr prior to 8.8.2, and the recommended action is to upgrade to this version or later.
Technical Analysis
The root cause of this vulnerability is a lack of validation in the ReplicationHandler's "masterUrl" parameter. Attackers may leverage this flaw to send requests that can manipulate the system's behavior, potentially causing it to access or expose sensitive internal resources. The attack vector is network-based with low complexity, requiring no special privileges or user interaction, which highlights the ease with which this flaw can be exploited.
In terms of impact, should an attacker successfully exploit this vulnerability, the consequences could include impacts on confidentiality, integrity, and availability, as the malicious requests could target resources that should remain protected. Therefore, organizations must take this threat seriously.
Risk & Impact Analysis
The real-world risk associated with CVE-2021-27905 is significant, especially for organizations deploying Apache Solr in environments that handle sensitive data or critical operations. The ability for attackers to exploit this vulnerability could have severe implications, including unauthorized data access or service disruption. The urgency for organizations to address this vulnerability is underscored by its critical CVSS score of 9.8, indicating high potential for exploitation and impact.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
All versions of Apache Solr prior to 8.8.2 are affected by this vulnerability. Organizations must ensure they are running this version or later to mitigate the risks associated with CVE-2021-27905.
Mitigation & Remediation
To mitigate this vulnerability, organizations must upgrade to Apache Solr version 8.8.2 or later. In cases where immediate patching is not feasible, organizations should consider implementing network controls to limit access to the Solr instance and monitor logs for any suspicious activity. For ongoing protection, regular security assessments and penetration testing can identify similar weaknesses in the system architecture. Organizations should validate remediation through penetration testing to ensure that all security measures are effective.
Detection Guidance
Monitoring for unusual request patterns or changes in Solr's behavior can help detect exploitation attempts. Organizations should review access logs for anomalies and set up alerts for suspicious activities related to the ReplicationHandler. Additionally, behavioral analysis can help identify potential exploitation attempts.
AppSecure Threat Intelligence Insight
CVE-2021-27905 illustrates the importance of thorough input validation in web applications. This vulnerability highlights the risks associated with SSRF vulnerabilities, which can have far-reaching consequences if left unaddressed. Security teams should focus on implementing comprehensive security practices, including regular assessments and updates to prevent similar vulnerabilities. For more information on securing your applications, organizations can refer to our resources on penetration testing methodology and vulnerability management programs that can help mitigate similar risks.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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