CVE-2018-20802

Post-auth queries on compound index may crash mongod

6.5 MediumFix available

A user authorized to perform database queries may trigger denial of service by issuing specially crafted queries with compound indexes affecting QueryPlanner. This issue affects MongoDB Server v3.6 versions prior to 3.6.9 and MongoDB Server v4.0 versions prior to 4.0.3.

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: Low
User interaction: None

What an attacker can affect

Confidentiality: None
Integrity: None
Availability: High

Exploit likelihood

1.58%Up 1.1 points since Apr 14, 2021

What each source reports

CVE List Score used 6.5

Post-auth queries on compound index may crash mongod

Record: CVE-2018-20802
CVSS 3.1: 6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-394
Updated: 2026-11-02

EUVDEUVD-2018-13344 6.5

Record: EUVD-2018-13344
CVSS 3.1: 6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-03

GitHub AdvisoriesGHSA-g6mr-mvf4-4wvj 6.5

A user authorized to perform database queries may trigger denial of service by issuing specially...

A user authorized to perform database queries may trigger denial of service by issuing specially crafted queries with compound indexes affecting QueryPlanner. This issue affects: MongoDB Inc. MongoDB Server v3.6 versions prior to 3.6.9, v4.0 versions prior to 4.0.3.

Record: GHSA-g6mr-mvf4-4wvj
CVSS 3.1: 6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-394
Updated: 2026-11-02

NVD 6.5

Record: CVE-2018-20802
CVSS 3.1: 6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CVSS 2.0: 4.0 MediumAV:N/AC:L/Au:S/C:N/I:N/A:P
Weakness: CWE-394
Updated: 2026-11-02

OSV 6.5

Record: CVE-2018-20802
CVSS 3.1: 6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVUBUNTU-CVE-2018-20802 6.5

Record: UBUNTU-CVE-2018-20802
CVSS 3.1: 6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVUSN-8064-1 No score

mongodb vulnerabilities

Eliot Horowitz discovered that MongoDB may fail to validate some instances of malformed BSON. A remote attacker could possibly use this issue to cause MongoDB to crash, resulting in a denial of service. This issue only affected Ubuntu 14.04 LTS. (CVE-2015-1609)

It was discovered that MongoDB read raw permissions from .dbshell history files. A local attacker could possibly use this issue to obtain sensitive information. This issue only affected Ubuntu 14.04 LTS and Ubuntu 16.04 LTS. (CVE-2016-6494)

Travis Brown discovered that MongoDB may be unable to parse specially crafted UTF-8 strings in BSON requests. A remote attacker could possibly use this issue to cause MongoDB to crash, resulting in a denial of service. This issue only affected Ubuntu 18.04 LTS. (CVE-2018-20802)

Record: USN-8064-1
Updated: 2026-11-02

Affected products

Affected packages

Affected packages
Package	Affected	Fixed
`mongodb` Ubuntu:Pro:18.04:LTS	before 1:3.6.3-0ubuntu1.4+esm1, plus listed versions 1:3.4.7-11:3.4.7-1ubuntu11:3.4.7-1ubuntu21:3.4.7-1ubuntu41:3.4.14-3ubuntu1 Show 5 moreShow less 1:3.4.14-3ubuntu21:3.6.3-0ubuntu11:3.6.3-0ubuntu1.11:3.6.3-0ubuntu1.31:3.6.3-0ubuntu1.4	1:3.6.3-0ubuntu1.4+esm1
`mongodb` Ubuntu:Pro:14.04:LTS	before 1:2.4.9-1ubuntu2+esm2, plus listed versions 1:2.4.6-0ubuntu51:2.4.6-0ubuntu61:2.4.8-1ubuntu11:2.4.8-21:2.4.9-11:2.4.9-1ubuntu11:2.4.9-1ubuntu2	1:2.4.9-1ubuntu2+esm2
`mongodb` Ubuntu:Pro:16.04:LTS	before 1:2.6.10-0ubuntu1+esm2, plus listed versions 1:2.6.10-0ubuntu1	1:2.6.10-0ubuntu1+esm2

History

History
Recorded	Changed	Sources
Nov 3, 2026	aliases, products, published	EUVD
Nov 2, 2026	first indexed	CVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2018-20802 is a medium vulnerability (CVSS 6.5) in Mongodb, published November 23, 2020. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.58%, the 75th percentile. Fixed in mongodb 1:3.6.3-0ubuntu1.4+esm1.