CVE-2020-20136: QuantConnect Lean versions from 2.3.0.0 to 2.4.0.1 are affected by an insecure deserialization vulnerability d

This week

CRITICAL 9.8REMOTEUPGRADE

CVE-2020-20136 is a critical-severity flaw (CVSS 9.8) affecting lean. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

QuantConnect Lean versions from 2.3.0.0 to 2.4.0.1 are affected by an insecure deserialization vulnerability due to insecure configuration of TypeNameHandling property in Json.NET library.

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.5% (top 25%)
CISA exploited list	No
Weakness	CWE-502
Published	2020-12-14
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: quantconnect

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2020-12-14 19:15 UTCPublished CVE record published
2026-06-17 03:02 UTCUpdated Record last modified

quantconnect lean UPGRADE

Affected: >= 2.3.0.0 and <= 2.4.0.1

Fixed in: newer than 2.4.0.1

Safe to downgrade to: a release before 2.3.0.0

1. Check installed version

apt-cache policy lean || rpm -q lean || lean --version

2. UPGRADE to newer than 2.4.0.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade lean

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade lean

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 2.3.0.0 (Debian / Ubuntu)

apt-cache madison lean sudo apt install lean=<VERSION_BEFORE_2.3.0.0> sudo apt-mark hold lean

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

dnf --showduplicates list lean sudo dnf downgrade lean-<VERSION_BEFORE_2.3.0.0> sudo dnf versionlock add lean

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-2020-20136?

lean: upgrade to newer than 2.4.0.1. Exact commands for each OS are on this page.

Is CVE-2020-20136 being exploited?

CVE-2020-20136 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-2020-20136 affect?

CVE-2020-20136 affects lean. Severity is critical (CVSS 9.8). QuantConnect Lean versions from 2.3.0.0 to 2.4.0.1 are affected by an insecure deserialization vulnerability due to insecure configuration of TypeNameHandling property in Json.NET library.

How urgent is CVE-2020-20136?

Priority 63/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

References

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