CVE-2026-57862 in Kanboard
Summary
by MITRE • 07/30/2026
Kanboard 1.2.52 and prior contains a server-side request forgery vulnerability that allows authenticated users to bypass SSRF protections by supplying hexadecimal IP address notation in user-controlled URLs. Attackers can submit hexadecimal-encoded internal IP addresses through the web link creation feature, causing cURL to resolve and connect to internal network resources such as cloud instance metadata services, localhost services, and RFC1918 addresses while the isPrivateURL() filter in app/Core/Http/Client.php incorrectly treats the input as safe due to FILTER_VALIDATE_IP rejecting non-dotted-decimal notation.
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Analysis
by VulDB Data Team • 07/30/2026
This vulnerability exists within Kanboard version 1.2.52 and earlier, representing a critical server-side request forgery flaw that undermines the application's security controls. The core issue stems from insufficient input validation in the URL handling mechanism, specifically within the app/Core/Http/Client.php file where the isPrivateURL() function fails to properly validate hexadecimal IP address notation. When authenticated users submit URLs containing hexadecimal-encoded internal IP addresses through the web link creation feature, the system's security measures are bypassed due to a fundamental flaw in the filtering logic.
The technical implementation of this vulnerability exploits the difference between how PHP's FILTER_VALIDATE_IP function processes various IP address formats and how cURL resolves these addresses internally. The filter specifically rejects non-dotted-decimal notation including hexadecimal representations, yet the application continues processing these inputs without proper sanitization. This creates a scenario where attackers can craft malicious URLs that appear to be valid but contain encoded internal network addresses such as 127.0.0.1 in hexadecimal format or RFC1918 private address ranges. The vulnerability operates at the intersection of CWE-918 Server-Side Request Forgery and CWE-20 Improper Input Validation, where the system's assumption about input safety is fundamentally flawed.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable full network reconnaissance and lateral movement within internal infrastructure. Attackers can leverage this flaw to access cloud instance metadata services such as AWS metadata endpoints, localhost services running on standard ports, and other internal resources that should remain isolated from external access. The vulnerability affects any authenticated user within the Kanboard application, which means that even limited privilege accounts could potentially exploit this weakness to gain insights into internal network topology and service configurations.
This security gap represents a significant risk to organizations relying on Kanboard for project management and collaboration, particularly in environments where network segmentation is critical. The flaw demonstrates a classic case of inadequate trust boundaries in web applications, where the application assumes that any input passing basic validation is safe to process without additional sanitization. Organizations using affected versions should immediately implement mitigation strategies including updating to patched versions, implementing network-level restrictions on outbound connections from the Kanboard server, and reviewing all URL handling mechanisms for similar vulnerabilities.
The vulnerability aligns with ATT&CK technique T1071.004 Application Layer Protocol: DNS, as it involves manipulation of URL resolution and network communication patterns to access internal resources. Additionally, it maps to ATT&CK technique T1566 Impersonation through the ability to forge requests that appear legitimate but actually target internal systems. The flaw also relates to ATT&CK technique T1046 Network Service Scanning as attackers can use this vulnerability to enumerate internal network services and infrastructure components.
Mitigation strategies should include immediate patching of the application to version 1.2.53 or later, where the vulnerability has been addressed through proper input validation and filtering mechanisms. Organizations should also implement additional controls such as network segmentation, outbound traffic restrictions, and monitoring for unusual URL patterns in web application logs. The fix typically involves strengthening the isPrivateURL() function to properly validate all IP address formats including hexadecimal notation, ensuring that cURL operations cannot be manipulated to access internal resources through malformed URL inputs. Regular security assessments should verify that similar vulnerabilities do not exist in other URL handling components throughout the application stack.
This vulnerability classification places it firmly within the category of high-severity issues that require immediate attention from security teams, as it directly enables unauthorized access to internal network resources that typically should remain protected from external exposure. The combination of authentication requirements with the ability to bypass SSRF protections creates a dangerous attack vector that can be exploited by both malicious insiders and external attackers who have gained initial access to the application environment.