CVE-2018-5241 in Advanced Secure Gateway
Summary
by MITRE
Symantec Advanced Secure Gateway (ASG) 6.6 and 6.7, and ProxySG 6.5, 6.6, and 6.7 are susceptible to a SAML authentication bypass vulnerability. The products can be configured with a SAML authentication realm to authenticate network users in intercepted proxy traffic. When parsing SAML responses, ASG and ProxySG incorrectly handle XML nodes with comments. A remote attacker can modify a valid SAML response without invalidating its cryptographic signature. This may allow the attacker to bypass user authentication security controls in ASG and ProxySG. This vulnerability only affects authentication of network users in intercepted traffic. It does not affect administrator user authentication for the ASG and ProxySG management consoles.
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Analysis
by VulDB Data Team • 03/17/2023
The vulnerability identified as CVE-2018-5241 represents a critical authentication bypass flaw affecting Symantec Advanced Secure Gateway versions 6.6 and 6.7, along with ProxySG versions 6.5 through 6.7. This issue stems from improper XML processing within the SAML authentication implementation, specifically when handling XML nodes containing comments. The vulnerability operates at the intersection of web security and identity management, where the system's failure to properly validate XML structure during SAML response parsing creates an exploitable gap in authentication controls. Organizations relying on these security appliances for network traffic interception and user authentication face significant risk exposure when this vulnerability is exploited.
The technical flaw manifests in the XML parsing mechanism's inability to correctly process XML nodes that contain comments, which allows attackers to manipulate SAML responses without breaking the cryptographic signatures that validate these responses. This weakness enables a sophisticated attack where an adversary can modify valid SAML assertions by injecting or altering XML comments within the response structure. The vulnerability specifically targets the authentication realm configuration that allows network users to be authenticated during intercepted proxy traffic processing. According to CWE-225, this represents an XML injection vulnerability where improper handling of XML constructs leads to security bypass conditions, while the ATT&CK framework categorizes this under credential access techniques involving authentication bypass through manipulation of authentication protocols.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it allows attackers to establish persistent unauthorized network access through intercepted traffic. Since the vulnerability specifically affects network user authentication within intercepted proxy traffic rather than administrative console access, attackers can potentially gain unauthorized access to network resources that would normally require proper authentication. This creates a scenario where network traffic can be decrypted and monitored without proper user authentication, potentially exposing sensitive data flows and enabling man-in-the-middle attacks. The attack vector requires a remote attacker with access to the network traffic being intercepted, making it particularly concerning for organizations with extensive proxy infrastructure.
Mitigation strategies for CVE-2018-5241 should focus on immediate patching of affected Symantec appliances to versions that properly handle XML comments in SAML responses. Organizations should also implement network segmentation to limit exposure of affected appliances and consider monitoring for unusual authentication patterns that might indicate exploitation attempts. The vulnerability's nature suggests that organizations should review their SAML authentication configurations and ensure proper XML validation is enforced at all levels of the authentication chain. Additionally, implementing network-based intrusion detection systems capable of identifying malformed SAML responses can provide early warning of potential exploitation attempts. Security teams should also conduct thorough vulnerability assessments to identify any other XML parsing components that might exhibit similar weaknesses and ensure that proper input validation is implemented across all authentication mechanisms.