How severe is CVE-2021-20727?

CVE-2021-20727 has a CVSS 3.x base score of 6.1, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2021-20727 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (60th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-20727?

CVE-2021-20727 affects Zettlr. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-20727?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-20727 published?

CVE-2021-20727 was published on 2021-05-27 and last updated on 2026-06-17.

CVE-2021-20727

CVE-2021-20727 is a medium-severity vulnerability in Zettlr with a CVSS 3.x base score of 6.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Medium (CVSS 3.x base score 6.1)
CVSS v2: 4.3
EPSS exploit prediction: 1% (60th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-79
Affected product: Zettlr
Published: 2021-05-27
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2021-20727?: 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 severe is CVE-2021-20727?: CVE-2021-20727 has a CVSS 3.x base score of 6.1, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2021-20727 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (60th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-20727?: CVE-2021-20727 affects Zettlr. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-20727?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-20727 published?: CVE-2021-20727 was published on 2021-05-27 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:zettlr:zettlr:*:*:*:*:*:*:*:*

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