CVE-2026-57940 in HTMLy
Summary
by MITRE • 06/26/2026
HTMLy 3.1.1 contains a Server-Side Request Forgery (SSRF) vulnerability in the RSS feed import functionality. The function get_feed() in system/admin/admin.php passes user-supplied $feed_url directly to file_get_contents() without any validation. An authenticated attacker with administrative privileges can exploit this by entering a crafted URL (e.g., http://dnslog.example.com, file:///etc/passwd, or http://169.254.169.254 in cloud contexts) via Tools -> Import RSS. The server will then make a request to the attacker-controlled target.
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Analysis
by VulDB Data Team • 06/26/2026
The HTMLy 3.1.1 application contains a critical server-side request forgery vulnerability that stems from improper input validation within its RSS feed import functionality. This vulnerability exists in the get_feed() function located in system/admin/admin.php where user-supplied feed_url parameters are directly passed to file_get_contents() without any sanitization or validation measures. The flaw represents a classic SSRF vector that allows authenticated administrative users to manipulate the application's outbound network requests, potentially exposing sensitive internal systems and data.
The technical implementation of this vulnerability demonstrates a fundamental failure in input validation practices where the application trust user-provided URLs without proper security checks. When an attacker navigates to Tools -> Import RSS and submits a malicious URL, the application processes the request through file_get_contents() which then establishes network connections to the specified targets. This behavior creates multiple attack vectors including DNS resolution requests that can be monitored for exfiltration purposes, local file inclusion attempts targeting system files like /etc/passwd, and cloud metadata service access such as the AWS EC2 metadata endpoint at 169.254.169.254 which provides sensitive instance information.
The operational impact of this vulnerability extends beyond simple data exposure to encompass potential lateral movement within network environments and privilege escalation opportunities. An attacker with administrative access can leverage this flaw to discover internal services, map network topology, and potentially extract cloud instance credentials or other sensitive metadata. The vulnerability directly maps to CWE-918 Server-Side Request Forgery (SSRF) which is categorized under the Common Weakness Enumeration framework as a critical security weakness. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1071.004 Application Layer Protocol: DNS where attackers can use such SSRF capabilities to perform reconnaissance and data exfiltration through DNS queries.
Mitigation strategies for this vulnerability must address both the immediate code-level fix and broader architectural security improvements. The primary remediation involves implementing strict input validation and URL sanitization within the get_feed() function, ensuring that only legitimate external URLs are accepted while blocking internal network addresses and restricted protocols. Organizations should implement URL whitelist mechanisms that validate against known good domains and reject any attempts to access internal IP ranges or special network addresses. Network-level protections including firewall rules and proxy configurations can also help prevent unauthorized outbound connections from the application server, creating additional defense-in-depth layers. Additionally, implementing proper authentication and authorization checks for administrative functions ensures that only legitimate users can access the RSS import functionality, reducing the attack surface for potential exploitation attempts.