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CVE-2021-39161

19
FAUCET Score

CVE-2021-39161 is a Cross-site Scripting (XSS) vulnerability in Discourse, an open-source community discussion platform, where category names can be leveraged for XSS attacks. This medium-severity vulnerability (CVSS 5.4) primarily affects Discourse instances where the default Content Security Policy (CSP) has been modified, disabled, or altered to allow moderators to modify categories, increasing the attack complexity. While patched in recent Discourse versions, there is no evidence of active exploitation, public exploit code, or significant community discussion surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
< 2.7.8CPE matchmatch criteria
cpe:2.3:a:discourse:discourse:*:*:*:*:*:*:*:*
2.8.0CPE matchmatch criteria
cpe:2.3:a:discourse:discourse:2.8.0:beta1:*:*:*:*:*:*
2.8.0CPE matchmatch criteria
cpe:2.3:a:discourse:discourse:2.8.0:beta2:*:*:*:*:*:*
2.8.0CPE matchmatch criteria
cpe:2.3:a:discourse:discourse:2.8.0:beta3:*:*:*:*:*:*
2.8.0CPE matchmatch criteria
cpe:2.3:a:discourse:discourse:2.8.0:beta4:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

4.4MEDIUM

CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:L/I:L/A:N

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
LOW
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality Impact
LOW
Integrity Impact
LOW
Availability Impact
NONE
Exploitability Score
1.3
Impact Score
2.7
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.41%
Probability of exploitation in next 30 days
EPSS Percentile
33.9%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0041 is in the 50th 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

Remediation records are not available for this CVE.

References

github.com / discourse/discourse/security/advisories/GHSA-xhmc-9jwm-wqph
Third Party Advisory