CVE-2020-23478: Leo Editor v6.2.1 was discovered to contain a regular expression denial of service (ReDoS) vulnerability in th

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HIGH 7.5REMOTEDOWNGRADE

CVE-2020-23478 is a high-severity flaw (CVSS 7.5) affecting leo. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Leo Editor v6.2.1 was discovered to contain a regular expression denial of service (ReDoS) vulnerability in the component plugins/importers/dart.py.

Why this priority

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

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.2% (top 31%)
CISA exploited list	No
Weakness	CWE-697
Published	2021-09-22
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: leoeditor

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

Am I affected?

Timeline

2021-09-22 20:15 UTCPublished CVE record published
2026-06-17 03:04 UTCUpdated Record last modified

leoeditor leo DOWNGRADE

Affected: 6.2.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 6.2.1

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 6.2.1 (Debian / Ubuntu)

apt-cache madison leo sudo apt install leo=<VERSION_BEFORE_6.2.1> sudo apt-mark hold leo

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list leo sudo dnf downgrade leo-<VERSION_BEFORE_6.2.1> sudo dnf versionlock add leo

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-2020-23478?

leo: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-23478 being exploited?

CVE-2020-23478 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-2020-23478 affect?

CVE-2020-23478 affects leo. Severity is high (CVSS 7.5). Leo Editor v6.2.1 was discovered to contain a regular expression denial of service (ReDoS) vulnerability in the component plugins/importers/dart.py.

How urgent is CVE-2020-23478?

Priority 53/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

References

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