How severe is CVE-2026-18691?

CVE-2026-18691 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-18691 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (27th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-18691?

CVE-2026-18691 primarily affects Mongodb. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-18691?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2026-18691 published?

CVE-2026-18691 was published on 2026-08-11 and last updated on 2026-09-16.

CVE-2026-18691

CVE-2026-18691 is a high-severity vulnerability in Mongodb with a CVSS 3.x base score of 8.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-757.

Key facts

Severity: High (CVSS 3.x base score 8.8)
CVSS v4: 9.0
EPSS exploit prediction: 0% (27th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-757
Affected product: Mongodb
Published: 2026-08-11
Last modified: 2026-09-16

Description

An issue in MongoDB Server's intra-cluster connection setup could allow a party with suitable network access to influence which authentication mechanism is used when one replica set member connects to another. Under certain conditions, this could cause the cluster's shared internal credential to be transmitted in a less-protected form, potentially allowing that credential to be recovered. If recovered, the credential could be used to authenticate as the internal superuser to nodes in the deployment.

Frequently asked questions

What is CVE-2026-18691?: An issue in MongoDB Server's intra-cluster connection setup could allow a party with suitable network access to influence which authentication mechanism is used when one replica set member connects to another. Under certain conditions, this could cause the cluster's shared internal credential to be transmitted in a less-protected form, potentially allowing that credential to be recovered. If recovered, the credential could be used to authenticate as the internal superuser to nodes in the deployment.
How severe is CVE-2026-18691?: CVE-2026-18691 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-18691 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (27th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-18691?: CVE-2026-18691 primarily affects Mongodb. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-18691?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2026-18691 published?: CVE-2026-18691 was published on 2026-08-11 and last updated on 2026-09-16.

References

https://jira.mongodb.org/browse/SERVER-130264

Affected products (4)

cpe:2.3:a:mongodb:mongodb:*:*:*:*:*:*:*:*
cpe:2.3:a:mongodb:mongodb:9.0.0:alpha0:*:*:-:-:*:*
cpe:2.3:a:mongodb:mongodb:9.0.0:alpha1:*:*:-:-:*:*
cpe:2.3:a:mongodb:mongodb:9.1.0:alpha0:*:*:-:-:*:*

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Other CWE-757 vulnerabilities

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CVE-2024-38883 — Critical (CVSS 9.1): An issue in Horizon Business Services Inc. Caterease 16.0.1.1663 through 24.0.1.2405 and possibly later versions,…
CVE-2019-14887 — Critical (CVSS 9.1): A flaw was found when an OpenSSL security provider is used with Wildfly, the 'enabled-protocols' value in the Wildfly…
CVE-2026-89177 — High (CVSS 8.8): WeenyGenius, a computer lab management system by Howyar Technologies, has a Use of Insecure Protocol vulnerability. Due…
CVE-2024-8773 — High (CVSS 8.3): SIMPLE.ERP client is vulnerable to MS SQL protocol downgrade request from a server side, what could lead to an…

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Threat intelligence

Threat-intel indicators referencing this CVE:

138.197.130.35 (ipv4-addr)
18.228.228.159 (ipv4-addr)
3.19.213.118 (ipv4-addr)