Security readout for executives and security teams
Plain-English summary
BigBlueButton 3.x versions before 3.0.20 can be tricked into redirecting users to an attacker-controlled site through an unvalidated errorRedirectUrl value. This does not directly compromise the server, but it can support phishing, credential theft, or user deception against trusted BigBlueButton deployments.
Executive priority
Prioritize normal patching for affected BigBlueButton 3.x systems. Escalate if the platform is public-facing, used by students or external users, or involved in sensitive authentication workflows. The risk is credible but not server takeover.
Technical view
CVE-2026-27736 is a CWE-601 open redirect in BigBlueButton ApiController. The errorRedirectUrl string is not validated before being used by respondWithRedirect. Affected versions are BigBlueButton >= 3.0.0 and < 3.0.20. CVSS 3.1 is 6.1, with network attack vector, low complexity, no privileges, and required user interaction.
Likely exposure
Exposure is limited to organizations running BigBlueButton 3.x before 3.0.20, especially internet-accessible virtual classroom portals. The main risk is users trusting a legitimate BigBlueButton link that redirects them to a malicious destination.
Exploitation context
The provided sources do not report active exploitation, and the CVE is not listed as KEV. Exploitation requires user interaction and is most relevant in phishing or social engineering scenarios where a victim follows a crafted BigBlueButton URL.
Researcher notes
The issue is source-described as direct use of an unvalidated errorRedirectUrl in respondWithRedirect. The public bundle names the fixing commit but does not provide evidence of exploitation or a workaround. Focus review on redirect validation and version verification, not assumptions about broader BigBlueButton branches.
Mitigation direction
- Upgrade BigBlueButton 3.x deployments to version 3.0.20 or later.
- Review vendor advisory GHSA-65cv-rg9f-qqrx for official remediation guidance.
- If upgrade timing is delayed, monitor vendor channels; no workaround is named in the sources.
Validation and detection
- Inventory BigBlueButton instances and identify any running versions 3.0.0 through 3.0.19.
- Confirm production systems are upgraded to BigBlueButton 3.0.20 or later.
- Review application logs for suspicious redirects involving errorRedirectUrl where logging is available.
- Validate user-facing links in phishing reports that involve BigBlueButton redirects.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-601: User-session and phishing behavior lookup
Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2026-27736 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 6.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N2.82.7Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.1MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/bigbluebutton/bigbluebutton/security/advisories/GHSA-65cv-rg9f-qqrxCVE reference · x_refsource_CONFIRM
- https://github.com/bigbluebutton/bigbluebutton/commit/691f92f3af0d6b796b91cb968977068663119812CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
URL Redirection to Untrusted Site ('Open Redirect')
URL Redirection to Untrusted Site ('Open Redirect') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.