Use After Free in MongoDB Server
CVE-2026-120809
A use-after-free read issue exists in MongoDB’s SBE (Slot-Based Execution) engine when processing aggregation pipelines with $unwind on time-series collections. An internal error in state-preservation logic can cause a value still referenced by downstream stages to have its underlying memory freed prematurely. An authenticated user can craft an aggregation pipeline under specific conditions to trigger this condition, potentially reading recycled server heap memory in query results or crashing the server. This issue is only triggerable when a non-default server parameter related to the SBE engine is enabled.
Vulnerability class: Use-After-Free
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.8 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:H.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
Weakness classification (CWE)
References
Frequently asked questions
- What is CVE-2026-120809?
- CVE-2026-120809 is a medium-severity vulnerability in MongoDB Server, classified under Use After Free. CVSS score: 6.8/10. Published 2026-11-10.
- How severe is CVE-2026-120809?
- Medium severity. CVSS v3 base score is 6.8 out of 10.