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CVE-2021-21283

19
FAUCET Score

CVE-2021-21283 is a cross-site scripting (XSS) vulnerability affecting the "Flarum Sticky" extension versions 0.1.0-beta.14 and 0.1.0-beta.15, an open-source discussion platform component. The vulnerability allows for HTML injection, enabling JavaScript execution from HTML attributes within the first post of a pinned discussion. This medium-severity vulnerability (CVSS 5.4) requires low privileges and user interaction, with potential impacts on confidentiality and integrity. There is no evidence of active exploitation, public exploit code, or significant community discussion, and it is not listed in CISA's KEV catalog.

Impacted Technologies

VendorProductVersion(s)CPE
0.1.0CPE matchmatch criteria
cpe:2.3:a:flarum:sticky:0.1.0:beta14:*:*:*:*:*:*
0.1.0CPE matchmatch criteria
cpe:2.3:a:flarum:sticky:0.1.0:beta15:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

5.4MEDIUM

CVSS:3.1/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
3.1

Exploit Intelligence

EPSS Score
0.79%
Probability of exploitation in next 30 days
EPSS Percentile
52.4%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0079 is in the 87th percentile among its peer group of 15,239 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.0 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 (2)

composerpatch availablevia ghsa
Product: flarum/stickyFixed in: 0.1.0-beta.15.1
github_advisorypatch availablevia nvd_reference
View patch

Vendor Advisories (1)

composerGHSA-h3gg-7wx2-cq3hmedium

XSS in Flarum Sticky extension

Jan 29, 2021

References

discuss.flarum.org / d/26042-security-update-to-flarum-sticky-010-beta151%29
github.com / flarum/sticky/commit/7ebd30462bd405c4c0570b93a6d48710e6c3db19
PatchThird Party Advisory
github.com / flarum/sticky/pull/24
PatchThird Party Advisory
github.com / flarum/sticky/security/advisories/GHSA-h3gg-7wx2-cq3h
Third Party Advisory