CVE-2018-15504 in GoAhead
Summary
by MITRE
An issue was discovered in Embedthis GoAhead before 4.0.1 and Appweb before 7.0.2. The server mishandles some HTTP request fields associated with time, which results in a NULL pointer dereference, as demonstrated by If-Modified-Since or If-Unmodified-Since with a month greater than 11.
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Analysis
by VulDB Data Team • 05/02/2023
This vulnerability exists in Embedthis GoAhead web server versions prior to 4.0.1 and Appweb versions prior to 7.0.2, representing a critical null pointer dereference flaw that can lead to service disruption. The issue specifically manifests when the server processes HTTP request fields related to time manipulation, particularly the If-Modified-Since and If-Unmodified-Since headers. When these headers contain month values exceeding 11, the server fails to properly validate the input data, resulting in a scenario where a null pointer is dereferenced during the parsing process. This behavior constitutes a classic buffer over-read condition that can be exploited by remote attackers to cause the web server to crash or become unresponsive, effectively creating a denial of service condition that impacts availability of the affected service.
The technical implementation of this vulnerability stems from inadequate input validation within the HTTP header processing logic of the web server software. The server's time parsing function does not properly sanitize month values in HTTP time headers, allowing values greater than 11 to pass through to the processing pipeline where they trigger a null pointer dereference. This flaw falls under the CWE-476 category of NULL Pointer Dereference, which is a well-documented weakness in software security that occurs when a program attempts to access a memory location through a pointer that has not been initialized to point to a valid memory location. The vulnerability demonstrates poor error handling and input validation practices that are commonly exploited in denial of service attacks.
From an operational impact perspective, this vulnerability poses significant risks to organizations relying on these web server implementations, particularly in environments where continuous availability is critical. The null pointer dereference can cause the web server process to terminate unexpectedly, requiring manual intervention to restart the service and potentially disrupting legitimate user access. Attackers can exploit this vulnerability by crafting malicious HTTP requests with malformed time headers, making it relatively easy to trigger the condition without requiring advanced technical skills or specific privileges. The vulnerability is particularly concerning because it can be exploited remotely without authentication, making it an attractive target for automated scanning and exploitation tools that are prevalent in the current threat landscape.
The mitigation strategy for this vulnerability requires immediate patching of affected systems to upgrade to versions 4.0.1 or later for GoAhead and 7.0.2 or later for Appweb, as these releases contain the necessary code fixes to properly validate time header inputs. Organizations should also implement network-level controls to monitor and potentially block HTTP requests containing suspicious time header values, though this approach should not be considered a substitute for proper patching. Security monitoring should include detection of abnormal server termination events and unusual traffic patterns that may indicate exploitation attempts. Additionally, system administrators should consider implementing intrusion detection systems that can identify and alert on crafted HTTP requests targeting this specific vulnerability, aligning with the ATT&CK technique T1499.004 for Network Denial of Service attacks. The vulnerability highlights the importance of robust input validation and proper error handling in web server implementations, emphasizing that even seemingly benign HTTP headers can be weaponized when not properly sanitized.