CVE-2017-2629 in macOS
Summary
by MITRE
curl before 7.53.0 has an incorrect TLS Certificate Status Request extension feature that asks for a fresh proof of the server's certificate's validity in the code that checks for a test success or failure. It ends up always thinking there's valid proof, even when there is none or if the server doesn't support the TLS extension in question. This could lead to users not detecting when a server's certificate goes invalid or otherwise be mislead that the server is in a better shape than it is in reality. This flaw also exists in the command line tool (--cert-status).
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Analysis
by VulDB Data Team • 01/05/2021
The vulnerability identified as CVE-2017-2629 represents a critical flaw in the curl command-line tool affecting versions prior to 7.53.0, specifically within the implementation of the TLS Certificate Status Request extension. This security weakness resides in the certificate validation logic where curl incorrectly processes the Certificate Status Request extension, which is designed to provide real-time proof of certificate validity through protocols such as OCSP (Online Certificate Status Protocol) or TLS-based certificate status information. The flaw manifests when curl encounters a server that supports the Certificate Status Request extension but fails to properly validate the responses, leading to a false positive scenario where the tool assumes certificate validity regardless of actual proof status. This issue directly impacts the security posture of users who rely on curl for secure communications, as it undermines the fundamental purpose of certificate validation mechanisms that are essential for detecting revoked or expired certificates.
The technical implementation of this vulnerability stems from improper handling of certificate status responses within curl's TLS validation code path. When curl connects to a server that supports the Certificate Status Request extension, the tool attempts to verify certificate status through the extension but fails to correctly interpret the responses from the server. The flaw creates a logical error where the certificate validation routine always returns a success status, even when no valid proof is received or when the server does not properly support the extension. This behavior occurs in both the library and command-line tool implementations, making the vulnerability pervasive across different usage contexts. The issue is particularly concerning because it operates at the protocol level where trust decisions are made, effectively bypassing the security checks that should detect certificate compromise or expiration.
The operational impact of CVE-2017-2629 extends beyond simple certificate validation failures to create a false sense of security for users of curl-based applications. When users execute curl commands with certificate status checking enabled, they receive misleading confirmation that certificates are valid even when they are not, potentially allowing attackers to exploit compromised certificates without detection. This vulnerability specifically affects the --cert-status command-line option and the underlying library functionality, making it particularly dangerous for automated security checking processes or applications that depend on curl for secure data transfer. The flaw essentially renders certificate status checking ineffective, which can lead to successful man-in-the-middle attacks or other security breaches where certificate validation should have prevented access. From an attacker's perspective, this vulnerability aligns with techniques described in the ATT&CK framework under T1552 (Unsecured Credentials) and T1071.004 (Application Layer Protocol: DNS) where compromised certificate validation can facilitate unauthorized access.
The security implications of this vulnerability can be analyzed through the lens of CWE-295, which addresses "Improper Certificate Validation," and CWE-310, which covers "Cryptographic Issues." The flaw demonstrates a failure in certificate validation logic that allows for false certificate status reporting, potentially enabling attackers to bypass security controls that depend on proper certificate validation. Organizations using curl for security-sensitive operations may experience undetected certificate compromise, leading to potential data breaches or unauthorized access to protected systems. The vulnerability particularly affects scenarios where certificate status checking is enabled, such as when using curl in automated security monitoring tools or when connecting to servers that implement certificate status request extensions. Remediation requires updating curl to version 7.53.0 or later, where the certificate status request handling has been corrected to properly validate responses and accurately reflect certificate status. System administrators should also consider implementing additional monitoring for certificate validation failures and ensure that all curl-based applications are updated to prevent exploitation of this validation bypass mechanism.