What is CVE-2021-3830?

CVE-2021-3830 is a medium-severity vulnerability in Btcpayserver Btcpay Server, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2021-09-26.

How severe is CVE-2021-3830?

Medium severity. CVSS v3 base score is 5.4 out of 10.

Is CVE-2021-3830 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

XSS in Btcpayserver Btcpay Server

CVE-2021-3830

btcpayserver is vulnerable to Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Vulnerability class: XSS (Cross-Site Scripting)

Published 2021-09-26 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.006 (45.5th percentile), scored 2026-10-20.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 45th percentile — 45.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: 0.000

Affected products

Btcpayserver Btcpay Server
Btcpayserver Btcpayserver/btcpayserver — versions unspecified

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

Public proof-of-concept exploits

b1nslashsh/CVE

References

github.com/btcpayserver/btcpayserver/commit/fc4e47cec608cc3dba24b19d0145ac69320… (Patch, Third Party Advisory)
huntr.dev/bounties/0fcdee5f-1f07-47ce-b650-ea8b4a7d35d8 (Exploit, Patch, Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2021-3830?: CVE-2021-3830 is a medium-severity vulnerability in Btcpayserver Btcpay Server, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2021-09-26.
How severe is CVE-2021-3830?: Medium severity. CVSS v3 base score is 5.4 out of 10.
Is CVE-2021-3830 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.