CVE-2026-77755 Denial of Service in MISP-STIX Import via Malformed or Oversized STIX Documents in misp-stix library
Attackers can cause denial of service in MISP-STIX importers by submitting malformed or oversized STIX documents that trigger unhandled exits or resource exhaustion.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-77755?
CVE-2026-77755 is a high-severity denial of service vulnerability in misp-stix, published on 21 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
A denial-of-service vulnerability was identified in misp-stix when processing attacker-controlled STIX 1 or STIX 2 documents.
The STIX import code used sys.exit() to handle several parsing and loading failures. Because SystemExit inherits from BaseException rather than Exception, these failures bypassed the exception handlers used by callers of the library. As a result, a malformed STIX document could terminate a long-running importer process instead of returning a recoverable parsing error.
Additionally, no limit was imposed on the size of STIX documents before parsing. A submitted document was therefore read and materialised in memory before its validity or type was evaluated. Depending on the document and parsing path, processing could consume approximately two to seven times the input size in memory, allowing a sufficiently large STIX document to cause excessive memory and CPU consumption and potentially terminate or severely degrade the importing service.
An attacker able to provide STIX content to a MISP-STIX import workflow could exploit either condition to affect availability. A malformed document could cause abnormal process termination through an uncaught SystemExit, while a large document could exhaust resources during deserialisation and conversion.
The fixes replace process-terminating sys.exit() calls with catchable exceptions such as STIXLoadingError and MissingSTIXContentError, and extend exception handling around the complete STIX detection and conversion process. The importer also now enforces an input-size limit before parsing. The default maximum is 100 MB, can be adjusted by callers, and can explicitly be disabled when required. STIX 1 inputs are additionally checked for the expected root element before the complete XML tree is constructed.
ImpactSuccessful exploitation can cause:
* termination of a long-running MISP-STIX importer; * excessive memory allocation; * excessive CPU consumption; * degradation or temporary unavailability of services relying on the converter; * interruption of batch or automated STIX ingestion workflows.
Weakness: CWE-400
Which versions are affected by CVE-2026-77755?
How do I fix CVE-2026-77755?
No fix has been published for CVE-2026-77755 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-77755 being exploited?
There is no known exploitation of CVE-2026-77755 in the wild and no public exploit code.
Sources
Also known as GHSA-65gx-wjvj-88j8.