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Fencer Vulns
medium 6.1

CVE-2021-34666 json

Add Sidebar <= 2.0.0 Reflected Cross-Site Scripting

published 2021-08-16 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-21316

cvss
6.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 58%
public exploits
0
none known

Summary

The Add Sidebar WordPress plugin is vulnerable to Reflected Cross-Site Scripting via the add parameter in the ~/wp_sidebarMenu.php file which allows attackers to inject arbitrary web scripts, in versions up to and including 2.0.0.

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
18 mo ago

Exploit prediction

0.84% chance of exploitation in the next 30 days, higher than 58% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • wordfence.com https://www.wordfence.com/vulnerability-advisories/#CVE-2021-34666 referenced PoC, tagged "exploit" by a source, unverified
  • plugins.trac.wordpress.org https://plugins.trac.wordpress.org/browser/sidebar-adder/tags/2.0.1/wp_sidebarMenu.php#L124 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
NVD 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:P/A:N

Affected products

  • Add Sidebar Add Sidebar

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation
Technology feeds

References

Sources

Fencer Vulns 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.