CVE-2021-39183
Unsafe inline XSS Owncast
Owncast is an open source, self-hosted live video streaming and chat server. In affected versions inline scripts are executed when Javascript is parsed via a paste action. This issue is patched in 0.0.9 by blocking unsafe-inline Content Security Policy and specifying the script-src. The worker-src is required to be set to blob for the video player.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- Low
- User interaction
- Required
What an attacker can affect
- Confidentiality
- Low
- Integrity
- High
- Availability
- Low
Exploit likelihood
What each source reports
CVE List Score used
Unsafe inline XSS Owncast
Owncast is an open source, self-hosted live video streaming and chat server. In affected versions inline scripts are executed when Javascript is parsed via a paste action. This issue is patched in 0.0.9 by blocking unsafe-inline Content Security Policy and specifying the script-src. The worker-src is required to be set to blob for the video player.
- Record
CVE-2021-39183- CVSS 3.1
- 8.2 High
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:H/A:L - Weakness
- CWE-79
- Updated
- 2026-11-02
EUVDEUVD-2021-2423
Owncast is an open source, self-hosted live video streaming and chat server. In affected versions inline scripts are executed when Javascript is parsed via a paste action. This issue is patched in 0.0.9 by blocking unsafe-inline Content Security Policy and specifying the script-src. The worker-src is required to be set to blob for the video player.
- Record
EUVD-2021-2423- CVSS 3.1
- 8.2 High
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:H/A:L - Updated
- 2026-11-03
GitHub AdvisoriesGHSA-2hfj-cxw7-g45p
Unsafe inline XSS in pasting DOM element into chat
Impact
Inline scripts are executed when Javascript is parsed via a paste action.
- Open https://watch.owncast.online/
- Copy and then paste
<img src=null onerror=alert('hello')>into the chat field. - An alert should pop up.
Patches
⋮ 13 │ // Content security policy
⋮ 14 │ csp := []string{
⋮ 15 │ "script-src 'self' 'sha256-2HPCfJIJHnY0NrRDPTOdC7AOSJIcQyNxzUuut3TsYRY='",
⋮ 16 │ "worker-src 'self' blob:", // No single quotes around blob:
⋮ 17 │ }
Will be patched in 0.0.9 by blocking unsafe-inline Content Security Policy and specifying the script-src. The worker-src is required to be set to blob for the video player.
For more information
If you have any questions or comments about this advisory:
- Open an issue in owncast/owncast
- Email us at [email protected]
- Record
GHSA-2hfj-cxw7-g45p- CVSS 3.1
- 8.2 High
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:H/A:L - Weakness
- CWE-79
- Updated
- 2026-11-02
NVD
Owncast is an open source, self-hosted live video streaming and chat server. In affected versions inline scripts are executed when Javascript is parsed via a paste action. This issue is patched in 0.0.9 by blocking unsafe-inline Content Security Policy and specifying the script-src. The worker-src is required to be set to blob for the video player.
- Record
CVE-2021-39183- CVSS 3.1
- 8.2 High
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:H/A:L - CVSS 3.1
- 6.1 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N - CVSS 2.0
- 4.3 Medium
AV:N/AC:M/Au:N/C:N/I:P/A:N - Weakness
- CWE-79
- Updated
- 2026-11-02
OSV
Owncast is an open source, self-hosted live video streaming and chat server. In affected versions inline scripts are executed when Javascript is parsed via a paste action. This issue is patched in 0.0.9 by blocking unsafe-inline Content Security Policy and specifying the script-src. The worker-src is required to be set to blob for the video player.
- Record
CVE-2021-39183- CVSS 3.1
- 6.1 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N - Updated
- 2026-11-02
OSVGHSA-2hfj-cxw7-g45p
Unsafe inline XSS in pasting DOM element into chat
Impact
Inline scripts are executed when Javascript is parsed via a paste action.
- Open https://watch.owncast.online/
- Copy and then paste
<img src=null onerror=alert('hello')>into the chat field. - An alert should pop up.
Patches
⋮ 13 │ // Content security policy
⋮ 14 │ csp := []string{
⋮ 15 │ "script-src 'self' 'sha256-2HPCfJIJHnY0NrRDPTOdC7AOSJIcQyNxzUuut3TsYRY='",
⋮ 16 │ "worker-src 'self' blob:", // No single quotes around blob:
⋮ 17 │ }
Will be patched in 0.0.9 by blocking unsafe-inline Content Security Policy and specifying the script-src. The worker-src is required to be set to blob for the video player.
For more information
If you have any questions or comments about this advisory:
- Open an issue in owncast/owncast
- Email us at [email protected]
- Record
GHSA-2hfj-cxw7-g45p- CVSS 3.1
- 8.2 High
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:H/A:L - Weakness
- CWE-79
- Updated
- 2026-11-02
OSVGO-2022-0291 No score
Unsafe inline XSS in pasting DOM element into chat in github.com/owncast/owncast
Unsafe inline XSS in pasting DOM element into chat in github.com/owncast/owncast
- Record
GO-2022-0291- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
github.com/owncast/owncastGo |
before 0.0.9 | 0.0.9 |
History
| Recorded | Changed | Sources |
|---|---|---|
| aliases | EUVD | |
| first indexed | CVE List, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2021-39183 is a high vulnerability (CVSS 8.2) in Owncast, published December 14, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.77%, the 55th percentile. Fixed in github.com/owncast/owncast 0.0.9.