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              "value": "\u003cp\u003eMISP 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\u0027s 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.\u003c/p\u003e"
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              "value": "\u003cp\u003eThe fix introduces a new validation function, check_required_taxonomy_tags_allowed, that iterates over every tag belonging to a required taxonomy and verifies each one is present in the configured allowed-tags list, raising a ForbiddenException if any tag is not allowed. This check is applied at both the event level and the attribute level. Additionally, an inherit_event_taxonomies flag is introduced so that attributes without their own required-taxonomy tags inherit the event\u0027s already-validated taxonomy, while attributes that do carry tags of the required taxonomy are still fully validated against the allowed list. This ensures that no non-allowed tag of a required taxonomy can pass the guard regardless of whether an allowed tag is also present.\u003c/p\u003e"
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      "title": "MISP Guard Incomplete Tag Validation Allows Non-Allowed Taxonomy Tags to Bypass Feed Policy Enforcement",
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                  "The CAPEC-120 mapping is the closest available match but is not a perfect fit; the attack involves manipulation of structured MISP event tag fields rather than traditional HTTP parameters. No more specific CAPEC for structured-data tag manipulation exists in the CAPEC catalog.",
                  "The CVSS PR:H assumption is based on the inference that an attacker needs write access to a MISP instance to author events with non-allowed tags. If the guard is deployed in a context where feed sources are fully trusted, the practical exploitability may be lower.",
                  "The exact fixed version is not specified in the patch metadata. The tag_version_boundary indicates v1.4 is the nearest tag with 15 commits after the fix, suggesting the fix landed in a version after 1.4, but the precise version number is unknown.",
                  "The SI:H rating assumes the data distribution policy violation (higher-TLP data reaching lower-TLP consumers) constitutes a significant integrity impact on the feed\u0027s trust model. A different rating (e.g., SI:L) could be argued if the policy is considered advisory rather than binding.",
                  "The patch does not specify whether the vulnerability was discovered through a security audit, bug report, or internal testing. No finder or reporter credit is assigned beyond the remediation developer."
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                    "rationale": "The closest plausible attack pattern is parameter tampering: an attacker who can author MISP feed events manipulates the tag parameters to include a non-allowed taxonomy tag (e.g., tlp:red) alongside an allowed one (e.g., tlp:clear), exploiting the guard\u0027s incomplete validation that only checked for the presence of at least one allowed tag. The uncertainty is that this is not a traditional HTTP parameter tampering scenario but rather manipulation of structured data fields (tags) within MISP event objects; however, the fundamental technique of altering input values to bypass validation aligns with CAPEC-120."
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                "patchSummary": "In src/mispguard.py: (1) Added a new method check_required_taxonomy_tags_allowed that loops over all tags of a required taxonomy and rejects any tag not in the allowed list. (2) Modified check_event_required_taxonomies to call the new method after the existing existence check. (3) Modified check_attribute_required_taxonomies to accept an inherit_event_taxonomies parameter; when True, the existence check is skipped (the event already satisfied it) but the new allowed-tags check still runs on any tags the attribute does hold. (4) Added the inherit_event_taxonomies parameter to check_attribute_level_rules and check_object_level_rules, threading it through recursive calls for ShadowAttribute and object attributes. (5) Updated check_required_taxonomy_exists to accept an entity parameter for clearer error messages. (6) Added 172 lines of test cases in src/test/test_misp_guard.py covering: event with both allowed and non-allowed taxonomy tags (blocked), untagged attribute under a tagged event (allowed), attribute in",
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              "value": "\u003cp\u003eMISP Guard, a proxy-based security filter for MISP 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.\u003c/p\u003e\u003cp\u003eAn 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 \u0027tlp\u0027 taxonomy with only \u0027tlp:clear\u0027 allowed, an event tagged \u0027TLP:AMBER\u0027 would not be recognized as belonging to the \u0027tlp\u0027 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 \u0027Person\u0027 would not match a configured block entry of \u0027person\u0027, allowing the attribute to pass through the filter.\u003c/p\u003e\u003cp\u003eThe 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.\u003c/p\u003e\u003cp\u003eThe 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.\u003c/p\u003e"
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