Regular Expression Denial of Service in Leo Editor

published 2021-09-22 5 y ago modified 2026-06-17 4 mo ago also GHSA-x38q-xg2h-rxgx , PYSEC-2021-338 , EUVD-2021-0108

cvss: 7.5; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 1.2%; EPSS 1.2% chance of exploitation in 30 days, percentile 69%
public exploits: 0; none known

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

Patch / fix

fixed in 1 links 2

pypi leo 6.3

github.com/leo-editor/leo-editor@0298336 commit
github.com/leo-editor/leo-editor/issues/1597 advisory

Exploit prediction

1.23% chance of exploitation in the next 30 days, higher than 69% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/leo-editor/leo-editor/issues/1597 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
NVD	3.1	7.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD	2.0	5.0	AV:N/AC:L/Au:N/C:N/I:N/A:P
GitHub	3.1	7.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem	package	affected	fixed in
pypi	leo	<6.3	6.3

Classification

Weakness

CWE-697 Incorrect Comparison
CWE-1333 Inefficient Regular Expression Complexity

References

github.com /leo-editor/leo-editor/issues/1597
web, exploit, issue-tracking, patch, third-party-advisory, report
github.com /leo-editor/leo-editor/commit/029833689060ee73f1bc1708cf4b182f0c66ec8e
web
cwe.mitre.org /data/definitions/1333.html
third-party-advisory
nvd.nist.gov /vuln/detail/CVE-2020-23478
advisory
github.com /advisories/GHSA-x38q-xg2h-rxgx
advisory
github.com /leo-editor/leo-editor
web
github.com /pypa/advisory-database/tree/main/vulns/leo/PYSEC-2021-338.yaml
web

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary