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High, CVSS 8.7amended

Opencast: Stored XSS in Paella player via WebVTT/DFXP caption cue text

CVE-2026-77615GHSA-m6c8-jcw2-5r25

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (org.opencastproject:opencast-engage-paella-player-7 20.2, 19.7; paella-core 1.50.6), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
8.7 · CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N
EPSS
  • CVE-2026-77615: 0.56% estimated exploitation activity in the next 30 days; percentile 46.61 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary The Opencast Paella player renders caption cue text into innerHTML without escaping. The captions canvas clears captionsContainer.innerHTML and then appends each active cue with captionsContainer.innerHTML += cue, so HTML inside a WebVTT or DFXP cue becomes live DOM and executes in the Opencast origin. The caption track is read from any media package element with a captions/ flavor and is served, with the player manifest, to anonymous viewers through /search/episode.json. The caption plugins that consume it are enabled in the default player configuration, the "Subtitles" upload that produces a captions/source track is active by default, and no caption processing step escapes the cue text. A user who can upload a subtitle to an event and publish it stores the payload in the published caption file. Any viewer who opens the event and turns captions on runs the script. Result: a non-admin content author stores JavaScript in a subtitle cue that executes in the browser session of…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-m6c8-jcw2-5r25

  2. Revision 2 · amended ·

    Amended from osv record GHSA-m6c8-jcw2-5r25

  3. Revision 1 · created ·

    Published from ghsa record GHSA-m6c8-jcw2-5r25

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-77615

Advisory: Opencast: Stored XSS in Paella player via WebVTT/DFXP caption cue text
IDs: CVE-2026-77615, GHSA-m6c8-jcw2-5r25
Record: https://patchnext.com/advisories/cve-2026-77615 (revision 3, source checked 26 Oct 2026, 13:02 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: org.opencastproject:opencast-engage-paella-player-7 20.2, 19.7; paella-core 1.50.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.opencastproject:opencast-engage-paella-player-7: affected < 19.7; >= 20.0, < 20.2; fixed in 20.2, 19.7
- npm paella-core: affected < 1.50.6; fixed in 1.50.6

## Suggested inspection (read-only)
- Maven org.opencastproject:opencast-engage-paella-player-7: check the installed version with your package manager.
- `npm ls paella-core --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on org.opencastproject:opencast-engage-paella-player-7, paella-core.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-m6c8-jcw2-5r25 (GitHub-reviewed advisory GHSA-m6c8-jcw2-5r25 lists affected ranges: npm paella-core >=0 <1.50.6)
- Verified: https://osv.dev/vulnerability/GHSA-m6c8-jcw2-5r25 (OSV record GHSA-m6c8-jcw2-5r25 lists affected ranges: Maven org.opencastproject:opencast-engage-paella-player-7 >=0 =20.0 =0 <1.50.6 (fixed))
- Verified: https://github.com/advisories/GHSA-m6c8-jcw2-5r25 (GitHub-reviewed advisory GHSA-m6c8-jcw2-5r25 lists affected ranges: Maven org.opencastproject:opencast-engage-paella-player-7 >=0 =20.0 =0 <1.50.6)

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