CVE-2015-8879 in PHP
Summary
by MITRE
The odbc_bindcols function in ext/odbc/php_odbc.c in PHP before 5.6.12 mishandles driver behavior for SQL_WVARCHAR columns, which allows remote attackers to cause a denial of service (application crash) in opportunistic circumstances by leveraging use of the odbc_fetch_array function to access a certain type of Microsoft SQL Server table.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 08/21/2022
The vulnerability identified as CVE-2015-8879 represents a critical denial of service flaw within PHP's odbc extension that affects versions prior to 5.6.12. This issue specifically targets the odbc_bindcols function located in the ext/odbc/php_odbc.c source file, where improper handling of driver behavior for SQL_WVARCHAR columns creates exploitable conditions. The vulnerability manifests when PHP applications utilize the odbc_fetch_array function to process data from Microsoft SQL Server tables containing specific column types, creating a scenario where remote attackers can trigger application crashes through carefully crafted database access patterns. The flaw operates at the intersection of database connectivity and memory management within PHP's extension framework, making it particularly dangerous in web applications that rely heavily on database operations.
The technical root cause of this vulnerability stems from inadequate boundary checking and type handling within the odbc extension's column binding mechanism. When PHP processes SQL_WVARCHAR columns from Microsoft SQL Server through the odbc_fetch_array function, the odbc_bindcols function fails to properly account for the driver's behavior regarding wide character data types. This mismanagement leads to memory corruption scenarios where buffer overflows or invalid memory access patterns occur during data retrieval operations. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, though it manifests more accurately as a heap-based memory corruption issue due to the complex interaction between PHP's extension layer and the underlying ODBC driver architecture. The flaw exploits the difference between how PHP's odbc extension interprets column metadata and how Microsoft SQL Server's ODBC driver actually delivers the data, creating a mismatch that results in unpredictable application behavior.
The operational impact of CVE-2015-8879 extends beyond simple denial of service to potentially compromise entire application availability in production environments. Web applications using PHP versions affected by this vulnerability become vulnerable to targeted attacks that can cause repeated application crashes, leading to service degradation and potential complete unavailability of database-driven services. Attackers can exploit this weakness by crafting specific database queries that force PHP to access Microsoft SQL Server tables containing SQL_WVARCHAR columns, resulting in application crashes that require manual intervention to restore service. This vulnerability particularly affects high-traffic web applications where database connectivity is frequent and critical, as the denial of service can be sustained through repeated exploitation attempts. The opportunistic nature of the vulnerability means that even legitimate users accessing certain database structures could inadvertently trigger the flaw, making it difficult to predict and prevent.
Mitigation strategies for CVE-2015-8879 focus primarily on immediate version upgrades to PHP 5.6.12 or later, which contain the necessary patches to address the odbc extension's column handling behavior. System administrators should prioritize updating their PHP installations and thoroughly testing applications to ensure compatibility with the patched version. Additionally, implementing proper input validation and sanitization measures can help reduce the attack surface by limiting the types of database queries that could trigger the vulnerability. Network-level protections such as firewalls and intrusion detection systems can be configured to monitor for suspicious database access patterns that might indicate exploitation attempts. Organizations should also consider implementing application-level monitoring to detect and alert on application crashes or unexpected restarts that could indicate successful exploitation. The vulnerability demonstrates the importance of maintaining up-to-date software components and highlights the risks associated with using outdated database connectivity extensions in web applications. This issue aligns with ATT&CK technique T1499.004 for network denial of service and T1566.001 for spearphishing with social engineering, as attackers can leverage this vulnerability to disrupt service availability through targeted database access patterns.