CVE-2015-3236 in cURL
Summary
by MITRE
cURL and libcurl 7.40.0 through 7.42.1 sends the HTTP Basic authentication credentials for a previous connection when reusing a reset (curl_easy_reset) connection handle to send a request to the same host name, which allows remote attackers to obtain sensitive information via unspecified vectors.
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Analysis
by VulDB Data Team • 02/01/2019
The vulnerability identified as CVE-2015-3236 affects cURL and libcurl versions between 7.40.0 and 7.42.1, representing a critical security flaw in HTTP authentication handling. This issue stems from improper credential management during connection reuse scenarios, specifically when utilizing the curl_easy_reset function to reset connection handles. The flaw manifests when a connection handle is reset and subsequently reused for requests to the same host, leading to the inadvertent transmission of authentication credentials from a previous connection. This behavior creates a significant information disclosure risk as attackers can potentially intercept and exploit these credentials to gain unauthorized access to protected resources. The vulnerability operates at the application layer and demonstrates a fundamental flaw in how authentication state is managed during connection lifecycle operations, particularly when handles are reset and reused rather than properly closed and reinitialized.
The technical implementation of this vulnerability involves the improper handling of HTTP Basic authentication credentials within the cURL library's connection management system. When curl_easy_reset is called on a connection handle, the library should ideally clear all authentication state and session information associated with that handle. However, in affected versions, the reset operation fails to properly clear HTTP Basic authentication credentials, allowing them to persist in memory and potentially be reused in subsequent requests. This occurs because the reset function does not properly invalidate the authentication context, creating a scenario where the same credentials can be sent to the server even when they should not be applicable to the new request. The flaw specifically impacts the HTTP Basic authentication mechanism and can be exploited through various attack vectors that involve connection reuse patterns, making it particularly dangerous in environments where persistent connections are utilized.
The operational impact of CVE-2015-3236 extends beyond simple credential leakage, as it can enable attackers to escalate privileges and access sensitive resources within applications that rely on cURL for HTTP communication. This vulnerability affects a wide range of applications and systems that utilize cURL or libcurl libraries for network operations, including web applications, automated scripts, and network monitoring tools. The information disclosure risk is particularly severe because HTTP Basic authentication credentials are transmitted in base64-encoded format, and if an attacker can intercept the traffic, they can easily decode and utilize these credentials to impersonate legitimate users. The vulnerability is especially concerning in environments where applications reuse connection handles for performance optimization, as this scenario is common in high-traffic web applications and API clients. The exploitability of this vulnerability is enhanced by the fact that it requires minimal attacker interaction beyond intercepting network traffic, making it a significant concern for organizations with sensitive data and applications that rely on HTTP Basic authentication.
Mitigation strategies for CVE-2015-3236 primarily involve upgrading to cURL version 7.42.2 or later, where the vulnerability has been addressed through proper credential clearing during connection reset operations. Organizations should conduct comprehensive vulnerability assessments to identify all systems and applications utilizing affected versions of cURL or libcurl, particularly those that implement HTTP Basic authentication. The remediation process should include not only software updates but also network monitoring to detect and prevent potential exploitation attempts. Additionally, security teams should consider implementing network segmentation and traffic monitoring to detect unauthorized credential transmission patterns. Organizations may also want to implement additional authentication mechanisms such as HTTP Digest authentication or token-based authentication to reduce the impact of credential exposure. This vulnerability aligns with CWE-200, which addresses information exposure, and represents a specific instance of improper credential handling that can be mitigated through proper library updates and security configuration practices. The ATT&CK framework categorizes this vulnerability under credential access and privilege escalation techniques, as it enables unauthorized access to protected resources through credential theft.