CVE-2023-33176: Blind SSRF When Uploading Presentation in BigBlueButton

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-06-26 · updated 2026-06-17
Weakness: CWE-918

Description

BigBlueButton is an open source virtual classroom designed to help teachers teach and learners learn. In affected versions are affected by a Server-Side Request Forgery (SSRF) vulnerability. In an `insertDocument` API request the user is able to supply a URL from which the presentation should be downloaded. This URL was being used without having been successfully validated first. An update to the `followRedirect` method in the `PresentationUrlDownloadService` has been made to validate all URLs to be used for presentation download. Two new properties `presentationDownloadSupportedProtocols` and `presentationDownloadBlockedHosts` have also been added to `bigbluebutton.properties` to allow administrators to define what protocols a URL must use and to explicitly define hosts that a presentation cannot be downloaded from. All URLs passed to `insertDocument` must conform to the requirements of the two previously mentioned properties. Additionally, these URLs must resolve to valid addresses, and these addresses must not be local or loopback addresses. There are no workarounds. Users are advised to upgrade to a patched version of BigBlueButton.

Affected products

bigbluebutton: before 2.5.18; from 2.6.0 before 2.6.9 — fixed in 2.5.18, 2.6.9

How to fix

Upgrade to a fixed version: bigbluebutton 2.5.18, 2.6.9. Check the vendor advisory for mitigations.

References

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