CVE-2026-110225 in Shaarli
Summary
by MITRE • 10/13/2026
Shaarli through 0.16.9 contains a server-side request forgery vulnerability that allows authenticated users to make the server request internal addresses by fetching bookmark thumbnails without private-address checks. Attackers can create bookmarks pointing to loopback, private, or cloud metadata addresses and trigger ThumbnailsController::ajaxUpdate or saving to send blind GET requests, with open_shaarli exposing this to any visitor.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability identified in Shaarli versions up to 0.16.9 represents a critical server-side request forgery flaw that exploits the application's bookmark thumbnail generation functionality. This issue stems from an insufficient validation of user-supplied input within the URL parsing logic, specifically failing to enforce strict restrictions on private or internal IP address ranges before initiating network requests. While many web applications implement basic checks against loopback addresses like 127.0.0.1, this implementation lacked comprehensive filtering for other reserved address spaces such as RFC 1918 private networks and cloud metadata endpoints. Consequently, an authenticated user can craft a bookmark entry with a URL pointing to internal infrastructure resources rather than public web content. When the application attempts to generate or update thumbnails for these bookmarks by invoking the ThumbnailsController::ajaxUpdate method or during standard save operations, it performs blind GET requests to the specified destination without verifying whether the target address is external and safe.
The operational impact of this vulnerability extends beyond simple internal network scanning due to two distinct attack vectors depending on the configuration state of the Shaarli instance. For instances where private bookmarking is disabled via the open_shaarli setting, any unauthenticated visitor can exploit this flaw by creating a malicious link that triggers an outbound request from the server. This transforms the vulnerability into a remote code execution enabler or data exfiltration vector accessible to attackers without valid credentials. In configurations where authentication is required, authenticated users with lower privileges can leverage their access level to probe internal services, potentially discovering sensitive administrative interfaces, database ports, or cloud instance metadata endpoints that are not exposed to the public internet but remain reachable from within the server's network namespace.
This flaw aligns closely with CWE-918 Server-Side Request Forgery (SSRF), which describes weaknesses where a web application fetches a remote resource without validating the user-supplied URL, allowing attackers to force the server to connect to arbitrary domains or ports. The exploitation technique also maps to MITRE ATT&CK techniques related to Network Service Discovery and Cloud Metadata API queries, as attackers can use the forged requests to enumerate internal services and extract sensitive configuration data such as IAM credentials from cloud metadata endpoints like 169.254.169.254. The lack of private-address checks means that even if external domains are restricted, the attacker retains significant capability to interact with local host resources or adjacent network segments, facilitating lateral movement within a compromised environment.
Mitigation strategies must prioritize strict input validation and output encoding for all URLs processed by the application. Developers should implement allow-listing mechanisms rather than block-listing when validating target hosts, ensuring that only explicitly permitted domains are accessible. Additionally, implementing network-level controls such as egress filtering or using a reverse proxy to restrict outbound connections from the web server can provide defense-in-depth against SSRF attacks. For existing deployments of Shaarli prior to version 0.16.9, immediate patching is recommended alongside reviewing access logs for signs of exploitation attempts targeting internal IP ranges. Administrators should also ensure that cloud metadata services are not accessible via standard HTTP from the application server and consider disabling thumbnail generation features if they are not essential to the specific use case, thereby reducing the attack surface available to potential adversaries.