CVE-2017-7668 in macOS
Summary
by MITRE
The HTTP strict parsing changes added in Apache httpd 2.2.32 and 2.4.24 introduced a bug in token list parsing, which allows ap_find_token() to search past the end of its input string. By maliciously crafting a sequence of request headers, an attacker may be able to cause a segmentation fault, or to force ap_find_token() to return an incorrect value.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 01/21/2021
The vulnerability identified as CVE-2017-7668 represents a critical buffer over-read flaw in the Apache HTTP Server software that emerged from the implementation of strict HTTP parsing mechanisms. This issue specifically affects versions 2.2.32 and 2.4.24 and later, where the developers introduced changes to enhance security by implementing stricter parsing of HTTP headers. The fundamental problem lies within the ap_find_token() function which is responsible for parsing token lists within HTTP header values. When processing malformed or specially crafted HTTP requests, this function fails to properly bounds-check its input parameters, leading to potential memory access violations.
The technical exploitation of this vulnerability occurs through the manipulation of HTTP request headers in a manner that causes the ap_find_token() function to traverse beyond the allocated memory boundaries of the input string. This improper bounds checking creates a condition where the function may read or write data beyond the intended memory region, potentially resulting in segmentation faults that crash the web server process. The flaw manifests when the parser encounters specific sequences of header values that cause it to iterate past the end of the input buffer, leading to unpredictable behavior that could be leveraged for denial of service attacks or potentially more severe consequences.
From an operational perspective, this vulnerability presents significant risks to web server availability and system stability. The segmentation fault condition can cause Apache httpd processes to crash repeatedly, leading to service disruption for legitimate users and potentially allowing attackers to perform sustained denial of service attacks against the affected servers. The impact extends beyond simple service interruption as the incorrect return values from ap_find_token() could potentially be exploited to bypass security mechanisms or manipulate server behavior in ways that might not be immediately apparent. This vulnerability particularly affects web servers that process large volumes of HTTP requests and rely heavily on header parsing for various server operations.
The mitigation strategies for CVE-2017-7668 primarily involve upgrading to patched versions of Apache HTTP Server where the buffer over-read issue has been resolved through proper bounds checking implementation. Organizations should prioritize immediate deployment of Apache 2.2.33 and 2.4.25 releases which contain the necessary fixes to address the token parsing vulnerability. Additionally, implementing proper input validation at the network level through firewalls and intrusion detection systems can provide an additional layer of protection while awaiting the deployment of official patches. Security monitoring should focus on detecting unusual patterns of HTTP request headers that might indicate exploitation attempts, as the vulnerability can potentially be used as part of broader attack campaigns targeting web infrastructure. This vulnerability aligns with CWE-129, which addresses improper validation of array index values, and can be categorized under ATT&CK technique T1499.004 for network denial of service attacks, demonstrating how seemingly minor parsing flaws can create significant security implications in web server environments.