CVE-2019-18657 in ClickHouse
Summary
by MITRE
ClickHouse before 19.13.5.44 allows HTTP header injection via the url table function.
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Analysis
by VulDB Data Team • 06/25/2025
The vulnerability identified as CVE-2019-18657 affects ClickHouse database management systems prior to version 19.13.5.44 and represents a critical HTTP header injection flaw that can be exploited through the url table function. This vulnerability falls under the category of improper input validation and occurs when the system fails to properly sanitize user-supplied input before incorporating it into HTTP headers during URL table function operations. The issue stems from inadequate sanitization of URL parameters that are processed through the table function mechanism, allowing malicious actors to inject arbitrary HTTP headers into the system's responses.
The technical implementation of this vulnerability involves the url table function which is designed to fetch data from remote URLs and present it as a table within ClickHouse. When a user provides a URL parameter to this function without proper validation, the system processes the input directly into HTTP headers without sufficient sanitization. This creates an injection vector where attackers can manipulate the HTTP response headers by crafting malicious URL inputs that contain header injection sequences. The flaw specifically impacts the HTTP response generation process, where the system's header construction logic fails to properly escape or validate characters that could be interpreted as header delimiters or injection commands.
From an operational perspective, this vulnerability poses significant risks to systems running vulnerable versions of ClickHouse as it can enable various attack vectors including but not limited to cache poisoning, cross-site scripting attacks, and potentially more severe header manipulation exploits. The impact extends beyond simple data exfiltration as attackers could manipulate response headers to redirect traffic, inject malicious content, or interfere with normal application behavior. This vulnerability is particularly dangerous in environments where ClickHouse serves as a data processing layer for web applications or where it handles untrusted user input through its table functions. The attack surface is broadened when the vulnerable system is exposed to external networks or when it processes data from untrusted sources through the url table function.
The vulnerability aligns with CWE-113, which describes improper neutralization of CRLF characters in HTTP headers, and can be categorized under ATT&CK technique T1071.004 for application layer protocol manipulation. Organizations utilizing ClickHouse should prioritize immediate patching to version 19.13.5.44 or later where the sanitization of URL parameters has been implemented to prevent header injection attacks. Additional mitigations include implementing strict input validation for all URL parameters, monitoring for unusual header patterns in system logs, and restricting access to the url table function to trusted users only. Network segmentation and web application firewalls can provide additional defense-in-depth measures while the primary remediation involves applying the vendor-provided security patch that addresses the root cause through improved input sanitization and header construction processes.