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Fencer Intel
medium 5.4

CVE-2021-3906 json

Unrestricted Upload of File with Dangerous Type in bookstackapp/bookstack

published 5y ago modified 4mo ago also EUVD-2021-27134

cvss
5.4
version 3.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.7%
EPSS 0.7% chance of exploitation in 30 days, percentile 52%
public exploits
0
none known

Summary

bookstack is vulnerable to Unrestricted Upload of File with Dangerous Type

Patch / fix

  • bookstackapp bookstackapp/bookstack 21.10.1

Is CVE-2021-3906 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Exploit prediction

0.67% chance of exploitation in the next 30 days, higher than 52% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • huntr.dev https://huntr.dev/bounties/f115bdf5-c06b-4627-a6fa-ba6904a43ba3 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.0 5.4 CVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
NVD 2.0 4.0 AV:N/AC:L/Au:S/C:P/I:N/A:N

Affected products

  • bookstackapp bookstackapp/bookstack

Classification

Weakness
  • CWE-434 Unrestricted Upload of File with Dangerous Type

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.