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Fencer Vulns
high 8.2

CVE-2021-39183 json

Unsafe inline XSS Owncast

published 2021-12-14 4 y ago modified 2026-07-08 4 mo ago also GHSA-2hfj-cxw7-g45p , GO-2022-0291 , EUVD-2021-2423

cvss
8.2
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 55%
public exploits
0
none known

Summary

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.

Patch / fix

  • go github.com/owncast/owncast 0.0.9
  • owncast_project owncast 0.0.9

Exploit prediction

0.77% chance of exploitation in the next 30 days, higher than 55% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/owncast/owncast/security/advisories/GHSA-2hfj-cxw7-g45p referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:H/A:L
NVD 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:P/A:N
GitHub 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:H/A:L

Affected packages

ecosystem package affected fixed in
go github.com/owncast/owncast
<0.0.9
0.0.9

Affected products

  • owncast owncast

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.