CVE-2026-85239: MISP Event Template Definition Validation Bypass Allows Persistent Denial of Service

DescriptionCVE.org

A vulnerability in MISP's event template handling allowed an authenticated user with permission to create or modify event templates to bypass validation of the template definition field. The EventTemplate::beforeValidate() method only performed semantic validation when the supplied definition was already represented as an array. If a caller instead supplied a pre-encoded string, including malformed JSON or JSON representing an unexpected data type, the value bypassed validateDefinition() and only needed to satisfy the generic notBlank validation rule. As a result, an invalid event template definition could be stored persistently in the database. When event templates were subsequently retrieved, EventTemplate::afterFind() attempted to decode the stored definition using JsonTool::decode() without handling decoding failures. A definition containing invalid JSON could therefore trigger an exception during retrieval. Because the event template index is available to all authenticated users, a single malicious or malformed template could make the event template listing and other functionality relying on EventTemplate queries return HTTP 500 errors until the offending database row was manually repaired. Valid JSON representing an unexpected type, rather than the expected JSON object, could similarly result in invalid data reaching downstream consumers. The vulnerability can therefore be exploited by a user capable of saving event templates to persist malformed template data and cause a persistent denial of service against event-template functionality for other users. The patch enforces that event template definitions must be supplied as structured objects before saving and always applies semantic validation. On retrieval, malformed JSON and definitions that do not decode to the expected structure are caught, logged, and replaced with an empty definition, preventing a malformed database entry from breaking all event template queries.

• misp · mispup to and including 2.5.45

Exploitation

Unlikely (under 1%). EPSS under 1%, or no score yet.

CISA KEV

Not listed

Public check

No public nuclei template

Weakness

Improper Input Validation · Input Validation and Logic

Vendor

misp

Published

September 2026

Band

Unlikely (under 1%), September 2026

• NVD entrynvd.nist.gov
• CVE recordcve.org
• Weakness CWE-20cwe.mitre.org
• Patchgithub.com