CVE-2018-10548 in PHP
Summary
by MITRE
An issue was discovered in PHP before 5.6.36, 7.0.x before 7.0.30, 7.1.x before 7.1.17, and 7.2.x before 7.2.5. ext/ldap/ldap.c allows remote LDAP servers to cause a denial of service (NULL pointer dereference and application crash) because of mishandling of the ldap_get_dn return value.
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Analysis
by VulDB Data Team • 03/08/2023
This vulnerability exists in PHP versions prior to the specified patches across multiple release lines including 5.6.x, 7.0.x, 7.1.x, and 7.2.x. The issue resides within the ext/ldap/ldap.c module which handles Lightweight Directory Access Protocol operations. When PHP applications interact with remote LDAP servers through the ldap_get_dn function, the code fails to properly validate the return value from this function before attempting to dereference it. This improper error handling creates a scenario where a malicious LDAP server can manipulate the response in such a way that causes PHP to attempt to dereference a NULL pointer, leading to an application crash and subsequent denial of service condition. The vulnerability represents a classic null pointer dereference flaw that can be exploited remotely without authentication, making it particularly dangerous in web applications that utilize LDAP authentication or directory services.
The technical execution of this vulnerability occurs when PHP's LDAP extension processes responses from remote servers. The ldap_get_dn function is designed to retrieve the distinguished name of an LDAP entry, but when the remote server returns an unexpected or malformed response, the function may return NULL. The vulnerable code does not check for this NULL return value before proceeding with operations that assume a valid pointer exists. This flaw maps directly to CWE-476 which specifically addresses NULL pointer dereference conditions in software implementations. The impact extends beyond simple application crashes to potentially affect entire web server processes, especially when PHP is running as a module within web servers like Apache or Nginx where multiple concurrent requests might be processed. Attackers can craft specially formatted LDAP responses that trigger this condition, effectively causing denial of service against applications that depend on LDAP functionality.
From an operational perspective, this vulnerability poses significant risk to web applications that integrate LDAP authentication or directory services, particularly those running on affected PHP versions. The denial of service impact means that legitimate users may be unable to access services that rely on LDAP for authentication, user management, or directory lookups. In enterprise environments where PHP applications interact with corporate LDAP directories, this vulnerability could be exploited to disrupt critical business operations. The remote nature of the attack means that attackers do not require local system access or prior authentication to exploit the vulnerability, making it a particularly attractive target for malicious actors. Additionally, the vulnerability affects multiple PHP release lines simultaneously, indicating it was a fundamental flaw in the LDAP extension implementation that persisted across several versions, requiring administrators to carefully assess their deployment environments and update accordingly.
The recommended mitigation strategy involves immediate patching of all affected PHP installations to the latest versions that contain the fix. Organizations should prioritize updating their PHP environments and verify that all applications using LDAP functionality are tested after the upgrade. Network segmentation and firewall rules can provide additional protection by limiting direct access to LDAP servers from web applications where possible. Monitoring and intrusion detection systems should be configured to detect unusual LDAP traffic patterns that might indicate exploitation attempts. Security teams should also consider implementing application-level controls that validate LDAP responses before processing them, providing an additional layer of defense beyond the core patch. The vulnerability demonstrates the importance of proper error handling in network-facing applications and highlights the need for comprehensive testing of third-party library integrations. Organizations should conduct thorough vulnerability assessments to identify all instances of affected PHP versions within their infrastructure and ensure that LDAP-related functionality is properly secured against such remote exploitation vectors.