CVE-2026-120811: Use-After-Free (CVSS 5.9)

Description

A use-after-free issue exists in the MongoDB server’s classic query engine plan cache. Under certain query conditions, an unowned reference to data from an earlier command can be retained in cached plan statistics. After the originating memory is freed, a subsequent diagnostic command serializing those statistics can read freed heap memory, potentially returning sensitive server process memory contents to the authenticated client. Under certain heap reuse conditions, this may also cause the server to crash.

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CVSS v3.1 Score

5.9

MEDIUM

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:L

EPSS — Exploit Prediction

0.0026

Probability of exploitation

0.18%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-416 Use After Free

References

Other References

https://jira.mongodb.org/browse/SERVER-135353

Frequently Asked Questions

What is CVE-2026-120811? +

A use-after-free issue exists in the MongoDB server’s classic query engine plan cache. Under certain query conditions, an unowned reference to data from an earlier command can be retained in cached plan statistics. After the originating memory is freed, a subsequent diagnostic command serializing those statistics can read freed heap memory, potentially returning sensitive server process memory contents to the authenticated client. Under certain heap reuse conditions, this may also cause the server to crash. It has a CVSS v3.1 base score of 5.9 (MEDIUM).

How severe is CVE-2026-120811? +

CVE-2026-120811 has a CVSS v3.1 score of 5.9 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0026, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-120811? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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