CVE-2021-33193 is a high-severity vulnerability found in Apache HTTP Server, specifically affecting versions from 2.4.17 to 2.4.48. This vulnerability allows a crafted method sent through HTTP/2 to bypass validation and be forwarded by mod_proxy. As a result, this may lead to request splitting or cache poisoning, which can significantly impact the integrity of the application. The CVSS score of 7.5 indicates that it poses a serious risk to organizations.
The exploitation status of this vulnerability is currently assessed as low, with no public exploits or proof-of-concept (PoC) code available. However, the potential for abuse remains, emphasizing the need for organizations to remain vigilant. Organizations should prioritize patching immediately to mitigate any risks associated with this vulnerability.
As the vulnerability is classified as high, organizations using affected versions should not delay in applying the necessary updates. The longer the vulnerability remains unpatched, the greater the risk of exploitation in real-world scenarios.
This vulnerability underscores the importance of maintaining an up-to-date patch management process. Security teams must continuously monitor for vulnerabilities, apply patches, and validate their effectiveness to protect against potential attacks.
Vulnerability Details
The vulnerability allows a crafted method sent through HTTP/2 to bypass validation and be forwarded by mod_proxy, which can lead to request splitting or cache poisoning. It has been given a CVSS score of 7.5, categorized as high severity due to its potential impact on the integrity of the system.
Affected products include Apache HTTP Server versions 2.4.17 to 2.4.48, with the vulnerability being publicly disclosed on August 16, 2021. Organizations using these versions should take immediate action to mitigate the risk.
Technical Analysis
The root cause of CVE-2021-33193 lies in the HTTP/2 handling within mod_proxy. The crafted method can bypass validation checks, allowing attackers to manipulate requests. This vulnerability operates over the network, requiring low attack complexity, and does not necessitate user interaction.
With no privileges required for exploitation, this vulnerability can be exploited by unauthenticated attackers. The integrity impact is classified as high, while confidentiality and availability impacts are none.
Risk & Impact Analysis
Risk to organizations includes potential cache poisoning and request splitting, which can lead to unauthorized access to sensitive information or manipulation of application behavior. Given the widespread use of Apache HTTP Server, the blast radius could be substantial if not addressed.
The urgency for remediation is high based on the CVSS score and the potential for exploitation. Organizations relying on affected versions should schedule remediation immediately to prevent potential exploitation.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The following versions of Apache HTTP Server are affected: 2.4.17 to 2.4.48. Organizations should ensure that they are running versions beyond this range to avoid exposure to this vulnerability.
Mitigation & Remediation
To mitigate CVE-2021-33193, organizations should apply the latest patches provided by Apache. It is crucial to update to versions beyond 2.4.48. For those unable to patch immediately, consider implementing additional network controls or configuration hardening to limit exposure.
Organizations can validate remediation effectiveness through penetration testing to identify similar weaknesses.
Detection Guidance
Organizations should monitor logs for unusual HTTP/2 methods and request patterns that deviate from normal behavior. Additionally, keep an eye on network signatures that may indicate exploitation attempts, as well as any unexpected changes to system configurations.
AppSecure Threat Intelligence Insight
The long-term significance of CVE-2021-33193 highlights the ongoing challenges associated with HTTP/2 and the necessity for robust validation mechanisms. This vulnerability represents a trend where improperly validated methods can lead to serious security issues.
Security teams should prioritize education on HTTP/2 vulnerabilities and maintain a proactive approach to patch management. Implementing continuous security testing can help identify and mitigate similar vulnerabilities before they can be exploited.
For more information on improving your security posture, organizations should consider resources such as the penetration testing methodology and the vulnerability management program design best practices.
Known Exploitation Timeline
This vulnerability is not currently listed in the Known Exploited Vulnerabilities (KEV) catalog, indicating that it has not been actively exploited in the wild.
EPSS Risk Context
The EPSS score for this vulnerability is 0.00739, placing it in the 72.85 percentile, suggesting a relatively low likelihood of exploitation compared to other vulnerabilities.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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