How severe is CVE-2021-26835?

CVE-2021-26835 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-2021-26835 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (67th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-26835?

CVE-2021-26835 affects Zettlr. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-26835?

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

When was CVE-2021-26835 published?

CVE-2021-26835 was published on 2021-06-18 and last updated on 2026-06-17.

CVE-2021-26835

CVE-2021-26835 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% (67th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-79
Affected product: Zettlr
Published: 2021-06-18
Last modified: 2026-06-17

Description

No filtering of cross-site scripting (XSS) payloads in the markdown-editor in Zettlr 1.8.7 allows attackers to perform remote code execution via a crafted file.

Frequently asked questions

What is CVE-2021-26835?: No filtering of cross-site scripting (XSS) payloads in the markdown-editor in Zettlr 1.8.7 allows attackers to perform remote code execution via a crafted file.
How severe is CVE-2021-26835?: CVE-2021-26835 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-2021-26835 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (67th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-26835?: CVE-2021-26835 affects Zettlr. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-26835?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-26835 published?: CVE-2021-26835 was published on 2021-06-18 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:zettlr:zettlr:1.8.7:*:*:*:*:*:*:*

More vulnerabilities in Zettlr

CVE-2021-20727 — 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…
CVE-2022-40276 — Medium (CVSS 5.5): Zettlr version 2.3.0 allows an external attacker to remotely obtain arbitrary local files on any client that attempts…

All CVEs affecting Zettlr →

Other CWE-79 (Cross-site Scripting (XSS)) vulnerabilities

CVE-2025-49410 — Critical (CVSS 10.0): Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in Imran Emu TC…
CVE-2024-47875 — Critical (CVSS 10.0): DOMPurify is a DOM-only, super-fast, uber-tolerant XSS sanitizer for HTML, MathML and SVG. DOMpurify was vulnerable to…
CVE-2024-6886 — Critical (CVSS 10.0): Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting') vulnerability in Gitea…
CVE-2023-45144 — Critical (CVSS 10.0): com.xwiki.identity-oauth:identity-oauth-ui is a package to aid in building identity and service providers based on…
CVE-2023-45138 — Critical (CVSS 10.0): Change Request is an pplication allowing users to request changes on a wiki without publishing the changes directly.…
CVE-2022-4361 — Critical (CVSS 10.0): Keycloak, an open-source identity and access management solution, has a cross-site scripting (XSS) vulnerability in the…

Browse all CWE-79 (Cross-site Scripting (XSS)) vulnerabilities →