CVE-2026-110223 in Kavita
Summary
by MITRE • 10/13/2026
Kavita 0.9.0 through 0.9.1.4 contains a server-side request forgery vulnerability that allows authenticated users to bypass the SSRF blocklist through DNS rebinding or HTTPS redirects. Attackers can submit a URL to POST /api/Cbl/upload-cbl-file whose host rebinds or redirects to internal addresses after validation, enabling blind internal port and service probing.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability identified in Kavita versions 0.9.0 through 0.9.1.4 represents a critical server-side request forgery flaw that undermines the integrity of network-level security controls designed to prevent unauthorized access to internal resources. This issue specifically affects authenticated users who possess valid credentials for the application, allowing them to exploit weaknesses in how the system validates and processes URLs submitted via the POST /api/Cbl/upload-cbl-file endpoint. The core technical failure lies in the server's inability to maintain a consistent validation state during asynchronous network operations involving DNS resolution or HTTP redirections. When an attacker submits a URL that initially points to an external, allowed domain, the server performs its security checks against this initial address and permits the request if it passes the blocklist criteria. However, because the Domain Name System allows for dynamic record updates, the hostname can resolve to different IP addresses over time or under specific conditions such as DNS rebinding attacks. Similarly, HTTPS redirects can be configured to point from an allowed external domain to a restricted internal address after the initial validation has already occurred but before the actual data transfer takes place.
This mechanism effectively bypasses the SSRF blocklist because the security control is applied only at the moment of request initiation rather than continuously throughout the lifecycle of the network connection. Once the server accepts the URL, it proceeds to fetch or upload content from the final destination IP address without re-verifying that this new target remains within the allowed scope. This flaw enables blind internal port and service probing, where an attacker can systematically scan internal networks by observing differences in response times, error messages, or application behavior when targeting different ports on internal hosts. Since the vulnerability is classified as a server-side request forgery, it leverages the trust relationship between the vulnerable web application and its backend infrastructure, allowing the attack to originate from within the trusted network perimeter rather than directly from an external source. This makes detection significantly more difficult for traditional intrusion prevention systems that rely on identifying malicious traffic patterns originating from outside the organization.
The operational impact of this vulnerability is substantial, as it grants authenticated attackers a foothold for deeper reconnaissance and potential lateral movement within the internal network. By probing internal services such as databases, administrative interfaces, or other microservices running on non-standard ports, an attacker can map out the internal architecture and identify additional targets with known vulnerabilities. In environments where Kavita is integrated with other systems that rely on similar upload mechanisms or trust relationships, this flaw could potentially be chained with other weaknesses to achieve remote code execution or unauthorized data exfiltration. The ability to bypass SSRF protections also violates fundamental security principles regarding the separation of trusted and untrusted network zones, exposing sensitive internal assets to risks typically mitigated by firewalls and access control lists that assume external requests cannot easily reach them.
To mitigate this vulnerability, organizations should immediately update Kavita to a version later than 0.9.1.4 where these validation logic flaws have been addressed. Until an upgrade is possible, network-level controls such as strict egress filtering can help limit the impact by preventing the server from initiating connections to private IP ranges regardless of how the request was formulated at the application layer. Additionally, implementing DNS rebinding protections on resolvers and ensuring that web applications perform final destination validation after all redirects have resolved are recommended defensive measures. From a classification perspective, this issue aligns with CWE-918 Server-Side Request Forgery (SSRF) due to its exploitation of server-side network interactions, and it maps to the ATT&CK technique T1572 Protocol Tunneling as attackers may use standard protocols like HTTP or DNS to establish covert channels for internal reconnaissance.