CVE-2018-5548 in BIG-IP APM
Summary
by MITRE
On BIG-IP APM 11.6.0-11.6.3, an insecure AES ECB mode is used for orig_uri parameter in an undisclosed /vdesk link of APM virtual server configured with an access profile, allowing a malicious user to build a redirect URI value using different blocks of cipher texts.
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Analysis
by VulDB Data Team • 05/16/2023
The vulnerability identified as CVE-2018-5548 affects F5 BIG-IP Access Policy Manager versions 11.6.0 through 11.6.3, representing a critical cryptographic weakness that undermines the security of authentication mechanisms. This flaw manifests within the APM virtual server configuration when access profiles are implemented, specifically targeting the handling of the orig_uri parameter within undisclosed /vdesk links. The vulnerability stems from the implementation of insecure AES ECB mode encryption for this particular parameter, creating a fundamental weakness in the cryptographic framework that protects user authentication flows.
The technical implementation of this vulnerability exploits the deterministic nature of Electronic Codebook (ECB) mode encryption, where identical plaintext blocks consistently produce identical ciphertext blocks. This characteristic allows malicious actors to analyze and manipulate encrypted data by constructing redirect URI values that leverage different cipher text blocks to achieve unauthorized access or redirection. The flaw specifically affects the orig_uri parameter which is used to maintain the original requested URI during authentication processes, making it a critical component in the authentication flow that can be manipulated by attackers. This vulnerability falls under CWE-327, which specifically addresses the use of insecure cryptographic algorithms, and more broadly under CWE-310, addressing cryptographic issues in general.
The operational impact of this vulnerability extends beyond simple authentication bypasses, as it enables attackers to potentially construct malicious redirect URIs that could lead to phishing attacks, session hijacking, or unauthorized access to protected resources. Attackers can leverage the predictable nature of ECB mode encryption to build crafted redirect values that manipulate the authentication flow, potentially redirecting users to malicious destinations while maintaining the appearance of legitimate authentication processes. This capability significantly undermines the trust model of the BIG-IP APM system and creates opportunities for advanced persistent threats to establish footholds within networks. The vulnerability aligns with ATT&CK technique T1566, which covers social engineering through spearphishing, as attackers can manipulate the redirect mechanisms to create convincing phishing campaigns.
Mitigation strategies for CVE-2018-5548 require immediate patching of affected BIG-IP APM systems to versions that address the insecure cryptographic implementation. Organizations should also implement network monitoring to detect suspicious redirect patterns and consider disabling the affected virtual server configurations until proper patches are applied. Security teams should conduct comprehensive vulnerability assessments to identify all instances of affected BIG-IP systems within their infrastructure, as the vulnerability affects a specific version range that may be present across multiple deployments. Additionally, implementing proper access controls and network segmentation can help limit the potential impact of successful exploitation attempts, while regular security audits should verify that cryptographic implementations follow industry standards such as those defined in NIST SP 800-38A for proper block cipher modes. The vulnerability demonstrates the critical importance of proper cryptographic implementation in authentication systems and the potential for seemingly minor cryptographic flaws to create significant security risks in enterprise environments.