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Fencer Intel
medium 4.9

CVE-2021-43099 json

An Archive Extraction (AKA "Zip Slip) vulnerability exists in bbs 5.3 in the UpgradeNow function in UpgradeManageAction.java, which unzips…

published 4y ago modified 4mo ago also EUVD-2021-30050

cvss
4.9
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.1%
EPSS 1.1% chance of exploitation in 30 days, percentile 66%
public exploits
0
none known

Summary

An Archive Extraction (AKA "Zip Slip) vulnerability exists in bbs 5.3 in the UpgradeNow function in UpgradeManageAction.java, which unzips the arbitrary upladed zip file without checking filenames. The vulnerability is exploited using a specially crafted archive that holds directory traversal filenames (e.g. ../../evil.exe).

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Exploit prediction

1.11% chance of exploitation in the next 30 days, higher than 66% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • github.com https://github.com/diyhi/bbs/issues/51 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 4.9 CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N
NVD 2.0 4.0 AV:N/AC:L/Au:S/C:N/I:P/A:N

Classification

Weakness
  • CWE-22 Improper Limitation of a Pathname to a Restricted Directory

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.