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CVE-2026-18691: An issue in MongoDB Server's intra-cluster connection setup could allow a party with suitable network access t

38
Routine
HIGH 8.8UPGRADEDOWNGRADE

CVE-2026-18691 is a high-severity flaw (CVSS 8.8) affecting mongodb, mongodb. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

  • High severity

A fixed release or distro patch exists.

Risk facts

CVSS score8.8 (High)
Attack vectorAdjacent network
Attack complexityLow
Privileges neededNone
User interactionNone
EPSS exploit chance0.4% (top 72%)
CISA exploited listNo
WeaknessCWE-757
Published2026-08-11
Last modified2026-10-23
Publisher (CNA): MongoDB, Inc. · Vendor: mongodb

Am I affected?

Timeline

mongodb mongodb UPGRADE
Affected: >= 7.0.0 and < 7.0.40 · >= 8.0.0 and < 8.0.29 · >= 8.2.0 and <= 8.2.12 · >= 8.3.0 and < 8.3.8
Fixed in: 7.0.40, 8.0.29, 8.3.8
Safe to downgrade to: a release before 7.0.0
1. Check installed version
apt-cache policy mongodb || rpm -q mongodb || mongodb --version
2. UPGRADE to 7.0.40 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade mongodb
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade mongodb
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
3. If no update is available yet, DOWNGRADE to a release before 7.0.0 (Debian / Ubuntu)
apt-cache madison mongodb sudo apt install mongodb=<VERSION_BEFORE_7.0.0> sudo apt-mark hold mongodb
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list mongodb sudo dnf downgrade mongodb-<VERSION_BEFORE_7.0.0> sudo dnf versionlock add mongodb
Downgrade risk
Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.
After downgrade
Restart the service, and keep the package held until a fixed release ships.
mongodb mongodb DOWNGRADE
Affected: 9.0.0 alpha0 · 9.0.0 alpha1 · 9.1.0 alpha0
Fixed in: no fixed release known
Safe to downgrade to: a release before 9.0.0
1. Check installed version
apt-cache policy mongodb || rpm -q mongodb || mongodb --version
2. No fixed release: DOWNGRADE to a release before 9.0.0 (Debian / Ubuntu)
apt-cache madison mongodb sudo apt install mongodb=<VERSION_BEFORE_9.0.0> sudo apt-mark hold mongodb
2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list mongodb sudo dnf downgrade mongodb-<VERSION_BEFORE_9.0.0> sudo dnf versionlock add mongodb
Downgrade risk
Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.
After downgrade
Restart the service, and keep the package held until a fixed release ships.
Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

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References

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