CVE-2026-78205 in BentoML
Summary
by MITRE • 08/24/2026
BentoML's outbound connection safeguard (make_safe_connect in _internal/utils/uri.py) blocks private, loopback, and link-local IP addresses but fails to reject the RFC 6598 shared address space (100.64.0.0/10, CGNAT). In versions 1.4.19 through 1.4.39, an unauthenticated attacker can supply URLs pointing to that range via multipart file handling (MultipartSerde.ensure_file) or JSON request parsing (JSONSerde.parse_request), causing the server to make outbound requests to internal hosts on CGNAT networks (Server-Side Request Forgery). This is an incomplete fix for CVE-2025-54381.
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Analysis
by VulDB Data Team • 08/24/2026
The vulnerability identified in BentoML versions 1.4.19 through 1.4.39 represents a critical Server-Side Request Forgery (SSRF) flaw stemming from an incomplete implementation of outbound connection safeguards. The core issue resides within the make_safe_connect function located in the _internal/utils/uri.py module, which is designed to prevent internal services from making unauthorized outbound network requests. While this safeguard successfully blocks connections to private IP ranges such as loopback addresses and link-local networks, it fails to account for the RFC 6598 shared address space, specifically the 100.64.0.0/10 range used for Carrier-Grade NAT (CGNAT). This oversight allows an unauthenticated attacker to bypass security controls by targeting internal hosts that reside within this specific IP block, effectively rendering the protection mechanism partially ineffective against a significant portion of private and shared network addresses.
The attack vector is facilitated through standard input processing mechanisms utilized by BentoML services. Specifically, attackers can exploit multipart file handling via MultipartSerde.ensure_file or JSON request parsing through JSONSerde.parse_request to inject malicious URLs pointing to CGNAT networks. By supplying these crafted inputs, an attacker forces the server to initiate outbound connections to internal infrastructure that would otherwise be inaccessible from external networks due to NAT boundaries. This capability allows for reconnaissance of internal services, potential data exfiltration if sensitive information is hosted on CGNAT-assigned hosts, or further pivoting into deeper network segments depending on the specific deployment architecture and connectivity between CGNAT ranges and other private subnets.
From a technical classification perspective, this vulnerability aligns with CWE-918 Server-Side Request Forgery (SSRF), as it involves an attacker influencing server-side network requests to access unintended resources. Furthermore, within the MITRE ATT&CK framework, this behavior corresponds to T1560.002 Data Staged via Archive Utility or potentially T1046 Network Service Discovery if used for scanning internal services. The vulnerability is explicitly noted as an incomplete fix for CVE-2025-54381, indicating that previous remediation efforts addressed only a subset of the affected address spaces but neglected to include RFC 6598 addresses in the blocklist logic. This partial mitigation creates a false sense of security while leaving critical internal assets exposed to remote exploitation by unauthenticated actors.
To mitigate this vulnerability, immediate action is required to update BentoML to version 1.4.40 or later where the make_safe_connect function has been corrected to include RFC 6598 addresses in its blocklist. In environments where an upgrade is not immediately feasible, network-level controls such as firewall rules should be implemented to restrict outbound connections from BentoML service hosts to the 100.64.0.0/10 range unless explicitly required for business operations. Additionally, input validation at the application layer should be strengthened to reject or sanitize any URLs containing IP addresses within this shared address space before they are processed by MultipartSerde or JSONSerde components. Regular security audits and penetration testing focusing on SSRF vectors are recommended to ensure that no other edge cases in URL parsing logic remain exploitable, thereby maintaining the integrity of internal network boundaries against external threats.