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CVE-2021-3646

22
FAUCET Score

CVE-2021-3646 describes a Cross-site Scripting (XSS) vulnerability in BTCPay Server, specifically affecting the btcpay_server product. This medium-severity flaw (CVSS 6.1) allows for improper neutralization of input during web page generation, meaning an attacker could inject malicious scripts into web pages viewed by other users. While the vulnerability requires user interaction (UI:R) and has low impact on confidentiality and integrity, there is currently no evidence of active exploitation, public exploit code, or significant community discussion surrounding it.

Impacted Technologies

VendorProductVersion(s)CPE
< 1.2.3CPE matchmatch criteria
cpe:2.3:a:btcpayserver:btcpay_server:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.0

4.9MEDIUM

CVSS:3.0/AV:A/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:L

Attack Vector
ADJACENT_NETWORK
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality Impact
LOW
Integrity Impact
LOW
Availability Impact
LOW
Exploitability Score
1.5
Impact Score
3.4
CvssVersion
3.0

Exploit Intelligence

EPSS Score
0.77%
Probability of exploitation in next 30 days
EPSS Percentile
51.9%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0077 is in the 59th percentile among its peer group of 26,221 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 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 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (1)

github_advisorypatch availablevia nvd_reference
View patch

References

github.com / btcpayserver/btcpayserver/commit/fc4e47cec608cc3dba24b19d0145ac69320b975e
PatchThird Party Advisory
huntr.dev / bounties/32e30ecf-31fa-45f6-8552-47250ef0e613
ExploitThird Party Advisory