CVE-2026-85239 MISP Event Template Definition Validation Bypass Allows Persistent Denial of Service
Authenticated users can bypass validation to store malformed event templates, causing persistent denial of service for other users.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-85239?
CVE-2026-85239 is a high-severity denial of service vulnerability in Misp-Project Misp, published on 3 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
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.
Poisoning doesn't seem reachable according to the lead developer.
Weakness: CWE-20
Which versions are affected by CVE-2026-85239?
It affects 1 product.
Products include Misp-Project Misp.
How do I fix CVE-2026-85239?
No fix has been published for CVE-2026-85239 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-2026-85239 being exploited?
There is no known exploitation of CVE-2026-85239 in the wild and no public exploit code.
Other vulnerabilities in Misp-Project Misp
Sources
Also known as GHSA-f9j4-826c-53wf.