How severe is CVE-2021-3767?

CVE-2021-3767 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2021-3767 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (44th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-3767?

CVE-2021-3767 affects Bookstackapp Bookstack. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-3767?

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

When was CVE-2021-3767 published?

CVE-2021-3767 was published on 2021-09-06 and last updated on 2026-06-17.

CVE-2021-3767

CVE-2021-3767 is a medium-severity vulnerability in Bookstackapp Bookstack with a CVSS 3.x base score of 5.4. 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 5.4)
CVSS v2: 3.5
EPSS exploit prediction: 1% (44th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-79
Affected product: Bookstackapp Bookstack
Published: 2021-09-06
Last modified: 2026-06-17

Description

bookstack is vulnerable to Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Frequently asked questions

What is CVE-2021-3767?: bookstack is vulnerable to Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
How severe is CVE-2021-3767?: CVE-2021-3767 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2021-3767 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (44th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-3767?: CVE-2021-3767 affects Bookstackapp Bookstack. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-3767?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-3767 published?: CVE-2021-3767 was published on 2021-09-06 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:bookstackapp:bookstack:*:*:*:*:*:*:*:*

More vulnerabilities in Bookstackapp Bookstack

CVE-2021-4119 — Critical (CVSS 9.8): bookstack is vulnerable to Improper Access Control
CVE-2020-5256 — High (CVSS 7.9): BookStack before version 0.25.5 has a vulnerability where a user could upload PHP files through image upload functions,…
CVE-2020-26211 — High (CVSS 7.7): In BookStack before version 0.30.4, a user with permissions to edit a page could insert JavaScript code through the use…
CVE-2020-26210 — High (CVSS 7.7): In BookStack before version 0.30.4, a user with permissions to edit a page could add an attached link which would…
CVE-2021-3944 — Medium (CVSS 6.8): bookstack is vulnerable to Cross-Site Request Forgery (CSRF)
CVE-2023-6199 — Medium (CVSS 6.5): Book Stack version 23.10.2 allows filtering local files on the server. This is possible because the application is…

All CVEs affecting Bookstackapp Bookstack →

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 →