CVE-2026-116469 in Guard
Summary
by MITRE • 10/26/2026
MISP Guard, a proxy-based security filter for MISP (Malware Information Sharing Platform) feed distribution, contains a case-sensitivity flaw in multiple policy enforcement checks. The functions check_required_taxonomy_exists, check_required_taxonomy_tags_allowed, check_blocked_attribute_categories, and check_blocked_analyst_data_sharing_groups_uuids performed case-sensitive string comparisons when matching event tags, attribute categories, and sharing-group UUIDs against configured allow/block lists.
An attacker with the ability to create or modify events in a MISP instance (or a connected instance that pushes events through the guard) could craft events using different letter case in taxonomy tag names, attribute categories, or sharing-group UUIDs to bypass the configured security policies. For example, if the policy requires the 'tlp' taxonomy with only 'tlp:clear' allowed, an event tagged 'TLP:AMBER' would not be recognized as belonging to the 'tlp' taxonomy and would therefore not be checked against the allowed-tags list, resulting in the event being forwarded to feed consumers. Similarly, a blocked attribute category such as 'Person' would not match a configured block entry of 'person', allowing the attribute to pass through the filter.
The security impact is unauthorized disclosure of threat-intelligence data that the operator intended to restrict. Events carrying non-allowed TLP (Traffic Light Protocol) markings, blocked attribute categories, or blocked sharing-group associations are forwarded to downstream feed consumers in violation of the configured distribution policy. This undermines the confidentiality controls that MISP Guard is designed to enforce.
The vulnerability is trivially exploitable: the attacker only needs to alter the letter case of a tag, category, or UUID string. No authentication beyond normal MISP event-creation privileges is required, and no user interaction is needed.
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Analysis
by VulDB Data Team • 10/26/2026
MISP Guard serves as a critical proxy-based security filter designed to enforce policy compliance within Malware Information Sharing Platform (MISP) feed distributions by validating events against configured allow and block lists before they are propagated to downstream consumers. The vulnerability identified in this system stems from a fundamental case-sensitivity flaw embedded within multiple core policy enforcement functions, specifically check_required_taxonomy_exists, check_required_taxonomy_tags_allowed, check_blocked_attribute_categories, and check_blocked_analyst_data_sharing_groups_uuids. These components are responsible for ensuring that events adhere to strict operational guidelines regarding taxonomy tags, attribute categories, and sharing group associations. However, the implementation relies on case-sensitive string comparisons when matching event metadata against these configured lists. This architectural oversight means that the security controls do not normalize input data before comparison, creating a predictable bypass vector where minor variations in character casing can effectively neutralize the intended restrictions.
The technical flaw allows an attacker with standard MISP event creation privileges to circumvent security policies by manipulating the letter case of specific identifiers within crafted events. For instance, if a policy mandates that only the tlp taxonomy is permitted and restricts it exclusively to the tlp:clear tag, an adversary can submit an event tagged as TLP:AMBER or TLP:RED. Because the comparison logic treats uppercase characters differently from their lowercase counterparts, the system fails to recognize these tags as belonging to the restricted tlp taxonomy category. Consequently, the validation checks are bypassed entirely, and the non-compliant event is forwarded to feed consumers without triggering any alerts or rejections. Similarly, if an operator has configured a block list for specific attribute categories such as person, submitting events with attributes categorized as Person will not match the blocked entry due to case mismatch, allowing sensitive data types to pass through the filter undetected.
The operational impact of this vulnerability is severe, resulting in the unauthorized disclosure of threat intelligence that security operators explicitly intended to restrict or monitor. MISP Guard is designed to act as a gatekeeper for confidentiality controls, ensuring that only compliant and safe data shares with external partners or internal teams. By bypassing these checks, attackers can leak high-sensitivity information, such as events marked with restrictive Traffic Light Protocol (TLP) markings like TLP:RED or TLP:AMBER, which are typically reserved for limited distribution to prevent widespread exposure of sensitive indicators. This breach undermines the integrity of the threat intelligence sharing ecosystem and violates organizational data governance policies. The vulnerability aligns with CWE-20 Improper Input Validation, as the system fails to adequately sanitize or normalize user-supplied input before processing it against security rules. Furthermore, this exploitation technique maps to MITRE ATT&CK tactic T1534 Internal Spearphishing if used for lateral movement within a trusted network, or more broadly to data exfiltration techniques where sensitive information is shared with unauthorized parties through manipulated metadata fields.
Exploitation of this vulnerability requires no authentication beyond the standard privileges needed to create or modify events in a MISP instance, nor does it require any user interaction from other system users. The attacker simply needs to alter the letter case of tag names, category labels, or sharing group UUIDs within their crafted payloads. This trivial exploitability makes the flaw particularly dangerous in environments where automated event ingestion is common and manual review of every incoming feed item is not feasible. To mitigate this risk, immediate remediation should focus on updating MISP Guard to enforce case-insensitive string comparisons for all policy enforcement checks involving taxonomy tags, attribute categories, and sharing group identifiers. Implementing input normalization routines that convert relevant metadata fields to a standard case format before validation would effectively close this bypass vector. Additionally, organizations relying on MISP Guard should consider implementing additional monitoring or logging mechanisms to detect anomalies in event tagging patterns until the software patch is deployed, ensuring that any potential exploitation attempts are identified and investigated promptly.