CVE-2026-81527: A NoSQL/expression injection weakness exists in the LINQ-to-aggregation query translation layer of the MongoDB

Routine

MEDIUM 6.5REMOTEUPGRADE

CVE-2026-81527 is a medium-severity flaw (CVSS 6.5) affecting c\# driver. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A NoSQL/expression injection weakness exists in the LINQ-to-aggregation query translation layer of the MongoDB C# Driver, in both aggregation expression and query filter translation. When application-supplied values are embedded in certain query constructs, special elements contained within those values are not properly escaped before the resulting query is transmitted to the database, so portions of the value may be interpreted by the database a

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 77%)
CISA exploited list	No
Weakness	CWE-943
Published	2026-08-27
Last modified	2026-09-29

Publisher (CNA): MongoDB, Inc. · Vendor: mongodb

Last updated 2026-09-29 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-27 20:18 UTCPublished CVE record published
2026-09-29 19:16 UTCUpdated Record last modified

mongodb c\# driver UPGRADE

Affected: >= 2.10.0 and < 3.11.1

Fixed in: 3.11.1

Safe to downgrade to: a release before 2.10.0

1. Check installed version

apt-cache policy c-driver || rpm -q c-driver || c-driver --version

2. UPGRADE to 3.11.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade c-driver

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade c-driver

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 2.10.0 (Debian / Ubuntu)

apt-cache madison c-driver sudo apt install c-driver=<VERSION_BEFORE_2.10.0> sudo apt-mark hold c-driver

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list c-driver sudo dnf downgrade c-driver-<VERSION_BEFORE_2.10.0> sudo dnf versionlock add c-driver

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.

Quick answers

How do I fix CVE-2026-81527?

c\# driver: upgrade to 3.11.1. Exact commands for each OS are on this page.

Is CVE-2026-81527 being exploited?

CVE-2026-81527 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-81527 affect?

CVE-2026-81527 affects c\# driver. Severity is medium (CVSS 6.5). A NoSQL/expression injection weakness exists in the LINQ-to-aggregation query translation layer of the MongoDB C# Driver, in both aggregation expression and query filter translation. When application-supplied values are embedded in certain

How urgent is CVE-2026-81527?

Priority 34/100. Remotely exploitable, no login, no user action

Software pages

MongoDB vulnerabilities

Related CVEs

CVE-2026-81528 MEDIUM 5.4 UPGRADE A MongoDB C# driver document-replacement code path omits the element-name/shape validation that the equivalent
CVE-2026-81529 HIGH 7.1 UPGRADE Improper neutralization of delimiters in connection-URL construction allows connection-option injection in the
CVE-2026-81530 MEDIUM 5.6 UPGRADE A weakness in the client-side encryption configuration surface of the MongoDB C# Driver causes sensitive key-m
CVE-2026-88025 HIGH 8.3 UPGRADE Improper neutralization of special elements in data query logic in the GridFS component of the MongoDB C# Driv
CVE-2026-88026 MEDIUM 6.5 UPGRADE Improper neutralization of regular-expression metacharacters in the LINQ query translation component of the Mo

References

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