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.
"}],"value":"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.\n\nAn 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.\n\nThe 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.\n\nThe 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."}],"impacts":[{"capecId":"CAPEC-10","descriptions":[{"lang":"en","value":"CAPEC-10 Parameter Tampering"}]}],"metrics":[{"cvssV4_0":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"NONE","attackVector":"NETWORK","baseScore":7.1,"baseSeverity":"HIGH","privilegesRequired":"LOW","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"NONE","valueDensity":"NOT_DEFINED","vectorString":"CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N","version":"4.0","vulnAvailabilityImpact":"NONE","vulnConfidentialityImpact":"HIGH","vulnIntegrityImpact":"NONE","vulnerabilityResponseEffort":"NOT_DEFINED"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]},{"format":"SSVC","other":{"content":{"options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"Supplier","timestamp":"2026-10-26T10:33:59Z","version":"2.0.3"},"type":"SSVC"},"scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-178","description":"CWE-178 Improper Handling of Case Sensitivity","lang":"en","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-20","description":"CWE-20 Improper Input Validation","lang":"en","type":"CWE"}]}],"providerMetadata":{"dateUpdated":"2026-10-26T10:35:51.992Z","orgId":"5a6e4751-2f3f-4070-9419-94fb35b644e8","shortName":"CIRCL"},"references":[{"name":"Security patch","tags":["patch"],"url":"https://github.com/MISP/misp-guard/commit/9868b1d93fc9cc40cc7c69ca11c86afd825bbc1c"}],"solutions":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"The fix makes all policy-matching comparisons case-insensitive by applying .lower() to both the input value (tag name, attribute category, sharing-group UUID) and the configured policy value (required taxonomy prefix, allowed tags, blocked categories, blocked UUIDs) before performing the comparison. This ensures that a tag such as 'TLP:AMBER' is correctly recognized as belonging to the 'tlp' taxonomy and is checked against the allowed-tags list, and that a blocked category or UUID is matched regardless of letter case.
"}],"value":"The fix makes all policy-matching comparisons case-insensitive by applying .lower() to both the input value (tag name, attribute category, sharing-group UUID) and the configured policy value (required taxonomy prefix, allowed tags, blocked categories, blocked UUIDs) before performing the comparison. This ensures that a tag such as 'TLP:AMBER' is correctly recognized as belonging to the 'tlp' taxonomy and is checked against the allowed-tags list, and that a blocked category or UUID is matched regardless of letter case."}],"title":"MISP Guard Case-Sensitive Policy Bypass Allows Unauthorized Feed Data Forwarding","x_gcve":[{"extensions":{"bcp-05-x-01":{"ai_annotations":[{"ai_level":"generated","description":"Draft vulnerability metadata was generated from a git-format patch using an Ollama-hosted language model. Human validation is required before publication.","gna_source":1,"models":[{"gna_source":1,"identifier":"qwen3.8:27b","name":"qwen3.8:27b","source":"ollama"}],"review_status":"partial","scope":"record","tags":["ai-computer-assisted:llm-generated","ai-computer-assisted:classification"]}]},"bcp-05-x-02":{"x_patch2vuln":{"assumptions":["The MISP Guard is assumed to operate as a proxy filtering outbound MISP feed data; the attacker is assumed to have the ability to create or modify events in a MISP instance that feeds through the guard. The patch does not specify the exact deployment topology.","PR:L assumes that creating events in MISP requires at least a low-privilege authenticated account. If the guard is used in a context where events are pushed from a connected MISP instance without per-event authentication, PR could be None.","The CAPEC-10 mapping is the closest available pattern; the actual attack involves modifying structured JSON event fields rather than traditional HTTP parameters, so the mapping is approximate.","No specific affected or fixed version numbers are provided in the patch metadata; the version range is marked as unspecified.","The commit message references 'ID 004' as a prior related fix, suggesting this is a follow-up to an earlier incomplete case-sensitivity fix, but no further details about that prior fix are available in the patch."],"capecRationale":[{"capecId":"CAPEC-10","rationale":"The attacker tampers with the letter case of tag names, attribute categories, or sharing-group UUIDs in MISP events to bypass the guard's policy checks. This is a form of parameter tampering where the input is modified in a way that the validation logic does not anticipate. CAPEC-10 is the closest available pattern; the uncertainty is that the tampering occurs in structured event data rather than in a traditional request parameter, but the underlying technique (modifying input to evade validation) aligns with this pattern."}],"commit":"9868b1d93fc9cc40cc7c69ca11c86afd825bbc1c","confidence":"medium","credits":[{"lang":"en","type":"remediation developer","value":"Luciano Righetti"},{"lang":"en","type":"remediation developer","value":"Claude Opus 5.5 (1M context)"},{"lang":"en","type":"tool","value":"Claude Opus 5.5 (1M context)"}],"cvssRationale":"AV:N: The MISP feed is consumed over the network (HTTP). AC:L: Exploitation requires only changing the letter case of a tag, category, or UUID string. AT:N: No log or audit tampering is needed. PR:L: The attacker needs the ability to create or modify events in a MISP instance, which typically requires a low-privilege user account or a connected instance. UI:N: No user interaction is required. VC:H: The primary impact is unauthorized disclosure of data that the operator intended to restrict (non-allowed TLP tags, blocked categories, blocked sharing groups are forwarded to feed consumers). VI:N: The data content is not modified, only improperly shared. VA:N: No availability impact. SC/SI/SA:N: No secondary system impact is evidenced.","fixSummary":"The fix makes all policy-matching comparisons case-insensitive by applying .lower() to both the input value (tag name, attribute category, sharing-group UUID) and the configured policy value (required taxonomy prefix, allowed tags, blocked categories, blocked UUIDs) before performing the comparison. This ensures that a tag such as 'TLP:AMBER' is correctly recognized as belonging to the 'tlp' taxonomy and is checked against the allowed-tags list, and that a blocked category or UUID is matched regardless of letter case.","generatedAt":"2026-10-26T10:33:59.935580Z","generator":"patch2vuln.py","model":"qwen3.8:27b","modelComparison":{"rankings":[{"agreementScore":11,"assumptionCount":5,"confidence":"medium","model":"qwen3.8:27b","score":7}],"selectedModel":"qwen3.8:27b","selectionMethod":"deterministic-consensus-v1","selectionNotice":"The selected result is closest to model consensus; this heuristic does not establish factual correctness and human review remains required."},"patchSha256":"26a847175a70394b7c0feaa57f7286f41fb131fc28c4c540412e88018c749628","patchSummary":"In src/mispguard.py, four comparison sites were changed: (1) check_required_taxonomy_exists now uses tag['name'].lower().startswith(required_taxonomy.lower() + ':') instead of a case-sensitive startswith; (2) check_required_taxonomy_tags_allowed applies .lower() to both the tag name and the required taxonomy prefix in the startswith check; (3) check_blocked_attribute_categories compares attribute['category'].lower() against a lowercased list of blocked categories; (4) check_blocked_analyst_data_sharing_groups_uuids compares the UUID in lowercase against a lowercased list of blocked UUIDs. Ninety-one lines of test cases were added to src/test/test_misp_guard.py covering mixed-case TLP tags in required-taxonomy checks and mixed-case blocked attribute categories.","patchTruncated":false,"patches":[{"commit":"9868b1d93fc9cc40cc7c69ca11c86afd825bbc1c","date":"Mon, 26 Oct 2026 10:25:52 +0100","patchSha256":"26a847175a70394b7c0feaa57f7286f41fb131fc28c4c540412e88018c749628","source":"https://github.com/MISP/misp-guard/commit/9868b1d93fc9cc40cc7c69ca11c86afd825bbc1c.patch","sourceUrl":"https://github.com/MISP/misp-guard/commit/9868b1d93fc9cc40cc7c69ca11c86afd825bbc1c.patch","subject":"fix: [security] match categories and required taxonomies"}],"source":"https://github.com/MISP/misp-guard/commit/9868b1d93fc9cc40cc7c69ca11c86afd825bbc1c.patch","ssvc":{"options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"Supplier","timestamp":"2026-10-26T10:33:59Z","version":"2.0.3"},"subject":"fix: [security] match categories and required taxonomies","weaknessRationale":[{"cweId":"CWE-178","rationale":"The root cause is that string comparisons used to enforce security policies (taxonomy prefix matching, category blocking, UUID blocking) were case-sensitive, allowing an attacker to bypass the checks by altering letter case. CWE-178 is the most specific and accurate mapping."},{"cweId":"CWE-20","rationale":"More broadly, the guard failed to validate input against the policy in a canonical form, which is a form of improper input validation. CWE-20 is included as a secondary, broader mapping."}]}},"bcp-05-x-03":{"x_timeline":{"events":[{"description":"Corrective change authored (9868b1d93fc9cc40cc7c69ca11c86afd825bbc1c): fix: [security] match categories and required taxonomies","id":"evt-fix-developed-1","references":["https://github.com/MISP/misp-guard/commit/9868b1d93fc9cc40cc7c69ca11c86afd825bbc1c.patch"],"timestamp":"2026-10-26T09:25:52Z","type":"fix-developed"}]}}},"recordType":"advisory","vulnId":"gcve-1-2026-20344"}]}},"cveMetadata":{"assignerOrgId":"5a6e4751-2f3f-4070-9419-94fb35b644e8","assignerShortName":"CIRCL","cveId":"CVE-2026-116469","datePublished":"2026-10-26T10:35:51.992Z","dateReserved":"2026-10-26T10:35:05.591Z","dateUpdated":"2026-10-26T10:35:51.992Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-10-26 11:16:37","lastModifiedDate":"2026-10-26 11:16:37","problem_types":["CWE-20","CWE-178","CWE-178 CWE-178 Improper Handling of Case Sensitivity","CWE-20 CWE-20 Improper Input Validation"],"metrics":{"cvssMetricV40":[{"source":"5a6e4751-2f3f-4070-9419-94fb35b644e8","type":"Secondary","cvssData":{"version":"4.0","vectorString":"CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","baseScore":7.1,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"NONE","privilegesRequired":"LOW","userInteraction":"NONE","vulnConfidentialityImpact":"HIGH","vulnIntegrityImpact":"NONE","vulnAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","exploitMaturity":"NOT_DEFINED","confidentialityRequirement":"NOT_DEFINED","integrityRequirement":"NOT_DEFINED","availabilityRequirement":"NOT_DEFINED","modifiedAttackVector":"NOT_DEFINED","modifiedAttackComplexity":"NOT_DEFINED","modifiedAttackRequirements":"NOT_DEFINED","modifiedPrivilegesRequired":"NOT_DEFINED","modifiedUserInteraction":"NOT_DEFINED","modifiedVulnConfidentialityImpact":"NOT_DEFINED","modifiedVulnIntegrityImpact":"NOT_DEFINED","modifiedVulnAvailabilityImpact":"NOT_DEFINED","modifiedSubConfidentialityImpact":"NOT_DEFINED","modifiedSubIntegrityImpact":"NOT_DEFINED","modifiedSubAvailabilityImpact":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED"}}],"ssvcV203":[{"source":"5a6e4751-2f3f-4070-9419-94fb35b644e8","ssvcData":{"timestamp":"2026-10-26T10:33:59Z","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"role":"Supplier","version":"2.0.3"}}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"116469","Ordinal":"1","Title":"MISP Guard Case-Sensitive Policy Bypass Allows Unauthorized Feed","CVE":"CVE-2026-116469","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"116469","Ordinal":"1","NoteData":"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.\n\nAn 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.\n\nThe 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.\n\nThe 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.","Type":"Description","Title":"MISP Guard Case-Sensitive Policy Bypass Allows Unauthorized Feed"}]}}}