CVE-2017-15710 in HTTP Server
Summary
by MITRE
In Apache httpd 2.0.23 to 2.0.65, 2.2.0 to 2.2.34, and 2.4.0 to 2.4.29, mod_authnz_ldap, if configured with AuthLDAPCharsetConfig, uses the Accept-Language header value to lookup the right charset encoding when verifying the user's credentials. If the header value is not present in the charset conversion table, a fallback mechanism is used to truncate it to a two characters value to allow a quick retry (for example, 'en-US' is truncated to 'en'). A header value of less than two characters forces an out of bound write of one NUL byte to a memory location that is not part of the string. In the worst case, quite unlikely, the process would crash which could be used as a Denial of Service attack. In the more likely case, this memory is already reserved for future use and the issue has no effect at all.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 02/24/2023
This vulnerability exists in Apache httpd versions ranging from 2.0.23 through 2.0.65, 2.2.0 through 2.2.34, and 2.4.0 through 2.4.29 and specifically affects the mod_authnz_ldap module when configured with the AuthLDAPCharsetConfig directive. The flaw stems from improper handling of the Accept-Language header value during LDAP authentication credential verification processes. When the module encounters an Accept-Language header value that does not exist in the configured charset conversion table, it attempts to apply a fallback mechanism that truncates the header value to a two-character representation to facilitate a quick retry. This truncation process becomes problematic when the original header value contains fewer than two characters, creating a condition where a null byte is written to memory locations outside the intended string boundaries.
The technical implementation issue manifests as an out-of-bounds memory write operation that occurs when processing header values with insufficient character length. This memory corruption vulnerability falls under the category of buffer over-read conditions and can potentially lead to arbitrary code execution or process termination depending on memory layout and system configuration. The vulnerability is classified as a memory safety issue that aligns with CWE-121 and CWE-125 categories, representing heap-based buffer overflow conditions that can be exploited through malformed input processing. The attack vector requires an authenticated user or system with access to the httpd server configuration to leverage the vulnerability effectively.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, though DoS remains the most likely outcome. While the probability of successful exploitation for privilege escalation or remote code execution is low, the potential for system instability and service disruption makes it a significant concern for web server administrators. The vulnerability affects systems that utilize LDAP authentication and have the mod_authnz_ldap module enabled with charset configuration, creating a potential attack surface for malicious actors seeking to disrupt web services. The issue demonstrates poor input validation and memory management practices that violate security best practices outlined in the OWASP Top Ten and MITRE ATT&CK framework's privilege escalation techniques. Organizations running affected Apache httpd versions should prioritize patching to prevent potential exploitation, as the vulnerability can be triggered through normal authentication requests.
The mitigation strategy involves upgrading to Apache httpd versions that have addressed this memory safety issue, specifically versions beyond the affected ranges mentioned in the CVE description. System administrators should also implement proper input validation for Accept-Language headers and consider disabling unnecessary authentication modules when not required. Additionally, monitoring for unusual authentication patterns and implementing intrusion detection systems can help identify potential exploitation attempts. The vulnerability serves as a reminder of the importance of proper memory management in security-critical components and the need for thorough testing of edge cases in input handling mechanisms. Organizations should conduct regular security assessments to identify and remediate similar issues in their web server configurations, particularly focusing on modules that handle external authentication protocols and user credential verification processes.