CVE-2016-8623 in macOS
Summary
by MITRE
A flaw was found in curl before version 7.51.0. The way curl handles cookies permits other threads to trigger a use-after-free leading to information disclosure.
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Analysis
by VulDB Data Team • 10/07/2022
The vulnerability identified as CVE-2016-8623 represents a critical use-after-free flaw in the curl library that affects versions prior to 7.51.0. This issue manifests when curl processes cookies in a multi-threaded environment where concurrent access to cookie data structures can lead to memory corruption. The flaw stems from improper synchronization mechanisms within curl's cookie handling implementation, creating a scenario where one thread may free memory while another thread attempts to access the same memory location, resulting in undefined behavior and potential information disclosure.
The technical root cause of this vulnerability aligns with CWE-416, which describes the use of freed memory condition. In curl's case, the cookie management system fails to properly protect shared cookie data structures from concurrent access patterns. When multiple threads operate simultaneously on cookie handling functions, the library does not implement adequate locking mechanisms to prevent race conditions. This allows an attacker to manipulate the timing of thread execution to force a scenario where freed memory is accessed, potentially leading to information leakage from other memory regions or even remote code execution depending on the specific memory layout and attack conditions.
From an operational perspective, this vulnerability poses significant risks to systems that rely on curl for HTTP communications, particularly in multi-threaded applications such as web servers, proxy services, and network monitoring tools. The information disclosure aspect can expose sensitive data including session tokens, authentication credentials, or other confidential information stored in memory. The vulnerability is particularly dangerous in environments where curl is used extensively for handling web requests and where applications may be running with elevated privileges or access to sensitive data repositories.
The impact of CVE-2016-8623 extends beyond simple information disclosure to potentially enable more sophisticated attacks through the use-after-free condition. Attackers can leverage this vulnerability to achieve arbitrary code execution by carefully controlling the memory layout and timing of thread operations. This aligns with ATT&CK technique T1059.007 for command and scripting interpreter and T1566 for credential harvesting, as compromised curl functionality can lead to both system compromise and data exfiltration. The vulnerability affects not only standalone curl applications but also any software that depends on curl's cookie handling capabilities, including web browsers, network security tools, and enterprise applications.
Organizations should prioritize immediate patching of all systems running curl versions prior to 7.51.0 to mitigate this vulnerability. The recommended mitigation involves upgrading to curl version 7.51.0 or later, which includes proper synchronization mechanisms for cookie handling. Additionally, administrators should implement monitoring for unusual cookie-related network activity and consider implementing application-level protections such as sandboxing or memory protection mechanisms. Security teams should also review their incident response procedures to ensure proper handling of potential exploitation attempts, as the vulnerability can be leveraged for both information disclosure and privilege escalation attacks.