CVE-2021-20727: Cross-site scripting vulnerability in Zettlr from 0.20.0 to 1.8.8 allows an attacker to execute an arbitrary s

Routine

MEDIUM 6.1UPGRADE

CVE-2021-20727 is a medium-severity flaw (CVSS 6.1) affecting zettlr. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Cross-site scripting vulnerability in Zettlr from 0.20.0 to 1.8.8 allows an attacker to execute an arbitrary script by loading a file or code snippet containing an invalid iframe into Zettlr.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	1.0% (top 36%)
CISA exploited list	No
Weakness	CWE-79
Published	2021-05-27
Last modified	2026-06-17

Publisher (CNA): JPCERT/CC · Vendor: zettlr

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

Am I affected?

Timeline

2021-05-27 09:15 UTCPublished CVE record published
2026-06-17 03:34 UTCUpdated Record last modified

zettlr zettlr UPGRADE

Affected: >= 0.20.0 and <= 1.8.8

Fixed in: newer than 1.8.8

Safe to downgrade to: a release before 0.20.0

1. Check installed version

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

2. UPGRADE to newer than 1.8.8 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade zettlr

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 0.20.0 (Debian / Ubuntu)

apt-cache madison zettlr sudo apt install zettlr=<VERSION_BEFORE_0.20.0> sudo apt-mark hold zettlr

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

dnf --showduplicates list zettlr sudo dnf downgrade zettlr-<VERSION_BEFORE_0.20.0> sudo dnf versionlock add zettlr

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-2021-20727?

zettlr: upgrade to newer than 1.8.8. Exact commands for each OS are on this page.

Is CVE-2021-20727 being exploited?

CVE-2021-20727 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-2021-20727 affect?

CVE-2021-20727 affects zettlr. Severity is medium (CVSS 6.1). Cross-site scripting vulnerability in Zettlr from 0.20.0 to 1.8.8 allows an attacker to execute an arbitrary script by loading a file or code snippet containing an invalid iframe into Zettlr.

How urgent is CVE-2021-20727?

Priority 37/100. No elevated risk signals yet.

Related CVEs

CVE-2022-40276 MEDIUM 5.5 DOWNGRADE Zettlr version 2.3.0 allows an external attacker to remotely obtain arbitrary local files on any client that a
CVE-2021-26835 MEDIUM 6.1 DOWNGRADE No filtering of cross-site scripting (XSS) payloads in the markdown-editor in Zettlr 1.8.7 allows attackers to

References

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