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Critical CVE-2021-40438 SSRF Vulnerability Alert: Apache HTTP Server Exploitation and Mitigation

CVE Image for report on CVE-2021-40438

Executive Summary

CVE-2021-40438 is a critical Server-Side Request Forgery (SSRF) vulnerability affecting Apache HTTP Server version 2.4.48 and earlier. This vulnerability allows a remote, unauthenticated attacker to force a vulnerable HTTP server to forward requests to arbitrary servers, potentially leading to unauthorized access to internal systems. The vulnerability has been actively exploited in the wild, making it imperative for organizations to take immediate action to mitigate the risk.

Technical Information

CVE-2021-40438 is a critical SSRF vulnerability identified in Apache HTTP Server versions up to and including 2.4.48. The vulnerability arises from the

mod_proxy
module, which can be manipulated by a crafted request URI-path to forward the request to an origin server chosen by the remote user. This flaw can be exploited by remote, unauthenticated attackers to gain unauthorized access to internal systems, bypassing firewalls and other security controls.

The vulnerability has been assigned a CVSS v3.1 Base Score of 9.0, indicating its critical nature. The vector for this vulnerability is CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H, which highlights its high impact on confidentiality, integrity, and availability.

The Common Weakness Enumeration (CWE) identifier for this vulnerability is CWE-918 (Server-Side Request Forgery (SSRF)). SSRF vulnerabilities are particularly dangerous because they allow attackers to send crafted requests from the vulnerable server to any destination, potentially accessing internal services and sensitive data.

Exploitation in the Wild

The CVE-2021-40438 vulnerability has been actively exploited in the wild. Attackers have been observed using this SSRF flaw to pivot through vulnerable servers and access internal networks. This exploitation allows them to bypass firewalls and other security controls, leading to unauthorized access to sensitive information and systems.

Specific instances of exploitation have been documented by various security organizations. For example, Cisco has issued a security advisory detailing the exploitation of this vulnerability (https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-2.4.49-VWL69sWQ). Additionally, the Cybersecurity and Infrastructure Security Agency (CISA) has included this vulnerability in its Known Exploited Vulnerabilities Catalog (https://www.cisa.gov/known-exploited-vulnerabilities-catalog).

Several proof-of-concept (PoC) exploits have been published on GitHub, demonstrating the ease with which this vulnerability can be exploited. These include: - Various Exploits for CVE-2021-40438 - Docker Exploit - Apache 2.4.48 SSRF Exploit - Sixpack Security Exploit - Xiaojiangxl Exploit

APT Groups using this vulnerability

While specific Advanced Persistent Threat (APT) groups exploiting this vulnerability have not been publicly identified, the nature of SSRF vulnerabilities makes them attractive to APTs for lateral movement and internal reconnaissance. APT groups often target sectors such as government, finance, healthcare, and critical infrastructure, leveraging vulnerabilities like CVE-2021-40438 to gain a foothold in targeted networks.

Affected Product Versions

The vulnerability affects the following software configurations: - Apache HTTP Server: Versions up to and including 2.4.48 - Siemens: - SINEC NMS: Versions up to (excluding) 1.0.3 - SINEMA Remote Connect Server: Versions up to (excluding) 3.1 - SINEMA Server: Version 14.0 - NetApp: - Cloud Backup: All versions - Clustered Data ONTAP: All versions - StorageGRID: All versions - Oracle: - HTTP Server: Versions 12.2.1.3.0 and 12.2.1.4.0 - Instantis Enterprisetrack: Versions 17.1, 17.2, 17.3 - Secure Global Desktop: Version 5.6 - ZFS Storage: All versions

Workaround and Mitigation

To mitigate this vulnerability, it is recommended to: 1. Update Apache HTTP Server: Upgrade to version 2.4.49 or later, where the vulnerability has been patched. 2. Configuration Changes: If an immediate upgrade is not possible, consider disabling the

mod_proxy
module or restricting its use to trusted backends only.

Vendor advisories provide additional guidance on mitigation strategies: - Apache Software Foundation: Apache HTTP Server 2.4 vulnerabilities - Siemens: SSA-685781 - NetApp: NTAP-20211008-0004 - Oracle: CPUAPR2022

References

Rescana is here for you

At Rescana, we understand the critical importance of staying ahead of emerging threats. Our Continuous Threat and Exposure Management (CTEM) platform is designed to help you identify, assess, and mitigate vulnerabilities like CVE-2021-40438. We are committed to providing you with the tools and insights needed to protect your organization from cyber threats. If you have any questions about this report or any other issue, please do not hesitate to contact us at ops@rescana.com.

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