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CVE-2026-77755 – Denial of Service – MISP-STIX (misp-stix) ≤ 2026.7.8

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Summary

CVE-2026-77755 is a denial-of-service vulnerability in misp-stix, the STIX import/export library used by MISP, affecting all versions up to and including 2026.7.8. Attacker-controlled STIX 1 or STIX 2 documents submitted to a MISP-STIX import workflow can crash the importer process or exhaust memory and CPU during deserialization. The issue carries a HIGH severity rating.

Technical details

  • Root cause #1: parsing/loading failures were handled with sys.exit(). Since SystemExit inherits from BaseException (not Exception), these calls bypassed the exception handlers used by callers, so a malformed document could kill a running importer process instead of raising a recoverable error.
  • Root cause #2: no size limit was enforced on STIX documents before parsing — input was fully read and materialized in memory before validity or type was checked, and processing could consume roughly 2–7x the input size in memory.
  • Trigger conditions: submission of a malformed STIX 1/2 document (triggers uncaught SystemExit) or a sufficiently large STIX document (triggers excessive memory/CPU consumption).
  • Attack vector: network — an attacker able to supply STIX content to a MISP-STIX import workflow, no privileges or user interaction required.
  • Impact: termination of a long-running MISP-STIX importer, excessive memory allocation, excessive CPU consumption, degradation or temporary unavailability of dependent services, and interruption of batch/automated STIX ingestion.

Affected software

  • misp-stix (MISP/misp-stix): all versions from 0 up to and including 2026.7.8

Severity

CVSS v4.0 Base Score: 8.7 (High)
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L
CWE-400: Uncontrolled Resource Consumption

Mitigation and recommended actions

  • Immediate: upgrade misp-stix to a version that includes the fix, which replaces process-terminating sys.exit() calls with catchable exceptions (STIXLoadingError, MissingSTIXContentError), extends exception handling around STIX detection/conversion, and enforces a default 100 MB input-size limit before parsing (adjustable or disableable by the caller). STIX 1 inputs are also validated for the expected XML root element before full tree construction.
  • If immediate patching isn’t possible: restrict or authenticate who can submit STIX documents to MISP import workflows, monitor importer processes for unexpected termination or abnormal memory/CPU spikes, and consider enforcing an upstream size limit on submitted STIX documents until upgraded.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Named response header set-cookie: MISP-
  • Raw response body: href="https://github.com/MISP/MISP"
  • URL of a loaded script: /js/misp.js

References

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