misp-stix CVE-2026-77755

Exploitation requires the ability to submit arbitrary STIX 1 or STIX 2 document content to a running misp-stix import workflow - typically via the MISP event import API, a STIX feed ingestion pipeline, or any integration that passes externally-sourced STIX files to the misp-stix library. For the sys.exit() termination condition, a malformed document that triggers any loading or parsing failure is sufficient; no specific file size is required. For the memory-exhaustion condition, a large STIX document is required, with effective memory cost at 2-7x raw input size depending on the parsing path (STIX 2 JSON is more expensive). Exploitation is limited by whether the STIX import endpoint is exposed to untrusted parties: MISP deployments that enforce API authentication before accepting imports, or that restrict STIX ingestion to internal or allowlisted sources, significantly reduce real-world risk. Both STIX 1 (XML) and STIX 2 (JSON) import paths are independently exploitable.

The CVSS 4.0 score of 8.7 (AV:N/AC:L/AT:N/PR:N/UI:N/VA:H/SA:L) reflects no authentication requirement and no special attack preconditions beyond network-reachable STIX import. The subsequent-system availability impact (SA:L) captures secondary service degradation beyond the importer process itself, such as batch ingestion pipelines stalling. There is no CISA KEV listing and no public POC identified at time of analysis, which tempers urgency; however, the attack primitives are trivially simple - crafting a malformed XML or JSON file or submitting a large file requires no exploit tooling. The PR:N rating in the provided CVSS 4.0 vector implies unauthenticated reachability of the STIX import path, but this depends on deployment: MISP instances that require API key authentication before accepting imports reduce the effective attack surface considerably. Real-world priority is moderate-to-high for organisations running automated or feed-driven STIX ingestion open to untrusted or semi-trusted sources; lower for deployments that gate imports behind authentication or restrict submission to internal systems.

An attacker with network access to a MISP instance that accepts STIX document imports submits either a crafted malformed STIX XML or JSON file that triggers a parsing failure, causing sys.exit() to raise an uncaught SystemExit that terminates the importer process, or submits a multi-gigabyte STIX bundle that forces the deserialiser to allocate 2-7x the file size in memory, exhausting host memory and CPU and degrading or crashing the importing service. No public proof-of-concept code has been identified, but both attack primitives require no special tooling beyond the ability to send HTTP requests or inject STIX content into a feed.