CVE-2026-116372 in Guard
Summary
by MITRE • 10/26/2026
MISP mispguard is a security filtering proxy that inspects and blocks MISP feed responses based on configured rules. The process_feed_response method in src/mispguard.py was responsible for evaluating feed responses before they reached the MISP instance. The original logic only explicitly handled the case where the HTTP status code was not 200 by passing the response through without filtering, on the assumption that non-200 responses would not carry ingestible event data. However, HTTP 2xx status codes other than 200 (such as 201 Created, 203 Non-Authoritative Information, and 206 Partial Content) were also passed through unfiltered. Because MISP may still ingest content from these responses, a malicious or compromised feed host could return a 203 or 206 status code with arbitrary content, effectively bypassing all of mispguard's filtering rules. This allowed unfiltered or malicious feed data to be ingested into the MISP instance, undermining the security controls that mispguard is designed to enforce. The vulnerability requires the attacker to control or compromise a feed endpoint configured in the MISP instance. No authentication or user interaction is required beyond the feed polling mechanism already in place.
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Analysis
by VulDB Data Team • 10/26/2026
The MisGuard component within the Malware Information Sharing Platform serves as a critical security filtering proxy, designed to inspect and block incoming data from external threat intelligence feeds based on administrator-configured rules. This intermediary layer is essential for maintaining the integrity of the MISP instance by ensuring that only validated and safe indicators are ingested into the system. The core logic responsible for this inspection resides in the process_feed_response method within the mispguard.py source file, which evaluates HTTP responses before they are passed to the main application for processing. A fundamental flaw exists in how this method determines whether a response should undergo filtering or be allowed through without scrutiny.
The vulnerability stems from an overly permissive logic condition that assumes only HTTP status code 200 OK contains ingestible event data, while all other non-200 responses are considered safe to bypass the filter because they presumably contain no useful content for ingestion. This assumption is technically flawed as it ignores the broader definition of successful HTTP transactions defined in RFC standards. Specifically, any response with a status code starting with 2, such as 201 Created, 203 Non-Authoritative Information, or 206 Partial Content, falls under the category of successful responses but was incorrectly treated by MisGuard as non-ingestible and therefore exempt from security checks. This oversight creates a significant gap in the defense-in-depth strategy employed by MISP administrators who rely on MisGuard to sanitize incoming threat intelligence.
An attacker with control over or access to one of the configured feed endpoints can exploit this logic error by returning an HTTP 2xx status code other than 200, such as 203 or 206, while including arbitrary malicious content in the response body. Since MisGuard bypasses filtering for these specific codes, the malicious payload is passed directly to MISP without inspection against configured blocklists or validation rules. This allows unfiltered and potentially harmful data to be ingested into the platform, undermining the security controls intended to protect the instance from compromised feeds. The impact includes potential corruption of threat intelligence databases, propagation of false positives, or execution of further attacks if the ingested content triggers downstream processing vulnerabilities within MISP itself.
This vulnerability is classified under CWE-20 Improper Input Validation and aligns with ATT&CK techniques related to Supply Chain Compromise, specifically T1588.004 which involves obtaining software through compromised feed sources. The attack vector requires no authentication or user interaction beyond the automated polling mechanism that MISP uses to fetch updates from configured feeds. Consequently, any system relying on MisGuard for security filtering remains vulnerable if it utilizes external feeds where an adversary can manipulate HTTP status codes. Mitigation strategies must focus on updating the mispguard.py logic to explicitly handle all 2xx status codes by applying standard filtering rules rather than bypassing them. Administrators should also consider implementing additional validation layers, such as content-type verification and signature checking, to ensure that only expected data formats are accepted regardless of the HTTP response code returned by upstream providers.