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CVE-2021-3906

23
FAUCET Score

CVE-2021-3906 describes an Unrestricted Upload of File with Dangerous Type vulnerability affecting BookStack, specifically bookstackapp bookstack. This medium-severity flaw (CVSS 6.5) allows an authenticated attacker to upload malicious files, potentially leading to high confidentiality impact without affecting integrity or availability. There is currently no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion or media coverage surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
< 21.10.1CPE matchmatch criteria
cpe:2.3:a:bookstackapp:bookstack:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.0

5.4MEDIUM

CVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality Impact
LOW
Integrity Impact
LOW
Availability Impact
NONE
Exploitability Score
2.3
Impact Score
2.7
CvssVersion
3.0

Exploit Intelligence

EPSS Score
0.65%
Probability of exploitation in next 30 days
EPSS Percentile
47.2%
Percentile rank of EPSS score among Peer Group
As of 2026-07-24
Model: v2026.06.15
This CVE's current EPSS score of 0.0065 is in the 57th percentile among its peer group of 21,924 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.1 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (1)

github_advisorypatch availablevia nvd_reference
View patch

References

github.com / bookstackapp/bookstack/commit/64937ab826b56d086af9ecea532510d37520ebc8
PatchThird Party Advisory
huntr.dev / bounties/f115bdf5-c06b-4627-a6fa-ba6904a43ba3
ExploitIssue TrackingPatchThird Party Advisory