CVE-2026-118173 in Guard
Summary
by MITRE • 10/27/2026
MISP Guard, a proxy that enforces security policies on MISP feed data, contained an incomplete validation check for required taxonomy tags. When a feed event or its attributes carried tags belonging to a required taxonomy (for example, TLP), the guard only verified that at least one tag of that taxonomy matched the configured allowed list. It did not verify that every tag of the required taxonomy present on the event or attribute was in the allowed list. As a result, an event or attribute could simultaneously carry an allowed tag (e.g., tlp:clear) and a non-allowed tag (e.g., tlp:red or tlp:amber) and still pass the guard's policy check. This allowed data marked with a higher classification or sensitivity level to be distributed through feeds configured to only distribute lower-classification data, effectively bypassing the intended data-handling restrictions. The vulnerability affected both event-level and attribute-level tag validation, including attributes nested within objects and shadow attributes. An attacker with the ability to author or modify MISP events in a feed source could include non-allowed taxonomy tags alongside allowed ones to exfiltrate more sensitive data to feed consumers than the guard policy intended to permit.
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Analysis
by VulDB Data Team • 10/27/2026
The vulnerability identified in MISP Guard stems from an incomplete validation logic within its proxy mechanism, which is designed to enforce security policies on Malware Information Sharing Platform (MISP) feed data. The core technical flaw lies in how the system processes taxonomy tags, specifically those related to Traffic Light Protocol classifications such as TLP:RED, TLP:AMBER, and TLP:CLEAR. When a feed event or its associated attributes contain tags belonging to a required taxonomy, the guard performs a check against a configured allowed list of acceptable values. However, this validation is logically insufficient because it only verifies that at least one tag from the specified taxonomy matches an entry in the allowed whitelist. It fails to iterate through and validate every single tag present on the event or attribute against the policy constraints. This oversight creates a logical bypass where mixed-tag scenarios are incorrectly deemed compliant.
In practical operation, this flaw allows for significant data handling violations. An attacker who has the ability to author or modify events within a MISP feed source can exploit this by including both an allowed tag and a non-allowed tag simultaneously on the same event or attribute. For instance, if a policy permits only TLP:CLEAR tags but rejects TLP:RED, an adversary could attach both tlp:clear and tlp:red to a single piece of intelligence. The MISP Guard would observe the presence of tlp:clear, determine that the allowed condition is met, and subsequently permit the data to pass through to feed consumers. Consequently, highly sensitive information marked with restrictive classifications like TLP:RED or TLP:AMBER can be distributed to systems configured exclusively for lower-classification data ingestion. This effectively nullifies the intended data-handling restrictions and leads to unauthorized exposure of confidential threat intelligence.
The scope of this vulnerability is broad, affecting both event-level and attribute-level tag validation processes. It encompasses attributes nested within objects as well as shadow attributes, which are often used in MISP for internal processing or secondary analysis without being directly exposed in the primary view. This comprehensive impact means that attackers can manipulate various layers of data structure to bypass controls. The operational impact is severe, as it undermines trust in automated threat sharing ecosystems where classification tags serve as critical safeguards against information leakage. Organizations relying on these feeds may inadvertently ingest sensitive indicators or malware samples they are not authorized to possess, potentially violating compliance standards and internal security policies regarding data segregation and access control.
From a cybersecurity framework perspective, this vulnerability aligns with CWE-20 Improper Input Validation, specifically the failure to validate all components of structured input against policy constraints. It also relates to CWE-693 Protection Mechanism Failure, as the protective mechanism designed to filter sensitive data is bypassed due to incomplete logic. In terms of MITRE ATT&CK techniques, this scenario reflects aspects of T1567 Exfiltration Over Web Service or Data Staged if viewed from the perspective of an attacker moving sensitive data out of a controlled environment through manipulated feeds. To mitigate this risk, it is imperative that MISP Guard be updated to implement strict validation logic that requires every tag belonging to a regulated taxonomy on any event or attribute to individually match the allowed list. Additionally, administrators should review existing feed configurations and audit historical events for potential exposure until patches are applied. Implementing rigorous input sanitization at the proxy level ensures that no mixed-classification data can slip through policy checks, thereby restoring the integrity of automated threat intelligence sharing protocols.