CVE-2021-3646Public exploitNetwork attack vector

Browser script execution via missing site-wide CSP

Published Sep 10, 2021 · Updated Aug 3, 2024

Reflected cross-site scripting in BTCPay Server before 1.2.3 allows remote attackers to execute script in a user's browser via crafted input. The referenced patch adds site-wide CSP with script nonces and hashes, but the public record does not identify the reflected parameter or rendering path. Exploitation requires user interaction and runs attacker-controlled script in the affected site's browser origin, exposing or altering accessible page data.

CVSS severity6.1
Medium
EPSS probability0.77%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Reflected cross-site scripting in BTCPay Server before 1.2.3 allows remote attackers to execute script in a user's browser via crafted input. The referenced patch adds site-wide CSP with script nonces and hashes, but the public record does not identify the reflected parameter or rendering path. Exploitation requires user interaction and runs attacker-controlled script in the affected site's browser origin, exposing or altering accessible page data.

The record

CVE
CVE-2021-3646
Published
Sep 10, 2021
Updated
Aug 3, 2024
Vendor
BTCPay Server
Product
BTCPay Server
Classifications
CWE-79, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 10, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <1.2.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

BTCPay Server · BTCPay Serverversion=unspecified <1.2.3

Published CVSS scores

4.3NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
4.9huntr.devCVSS:3.0/AV:A/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:L
6.1NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo