EUVD-2026-44996Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
Requires an existing valid session so PR:L; network-reachable token prediction with no user interaction; impersonation breaks confidentiality and integrity (C:H/I:H) but not availability.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
Lifecycle Timeline
4DescriptionCVE.org
BigBlueButton is an open-source virtual classroom. Prior to 3.0.21, bbb-web generated conference sessionToken values with insufficiently secure randomness in bbb-common-web/src/main/java/org/bigbluebutton/api/Util.java and bigbluebutton-web/grails-app/controllers/org/bigbluebutton/web/controllers/ApiController.groovy, allowing a session user to predict other users' conference session tokens and impersonate them. This issue is fixed in version 3.0.21.
AnalysisAI
Session hijacking in BigBlueButton before 3.0.21 lets an authenticated conference participant predict and reuse other users' session tokens to impersonate them. The bbb-web component generated 16-character sessionToken values (and 12-character auth tokens and internal user IDs) using Apache Commons RandomStringUtils.randomAlphanumeric, a non-cryptographic PRNG, making the token space guessable to anyone who already holds a valid session. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | The attacker must first hold a valid conference session on the target BigBlueButton server (PR:L) - i.e., be able to join a meeting as a participant - because prediction relies on the same weak java.util.Random-based generator that issues tokens for other users. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 vector (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N, score 8.1) indicates network-reachable, low-complexity exploitation by an attacker who already holds low-level privileges - i.e., a legitimate session user, which matches the description of 'a session user' predicting others' tokens. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker joins a meeting as an ordinary participant, obtaining a valid session and observing the format and values of issued tokens. Knowing that tokens come from a non-cryptographic java.util.Random, the attacker predicts another participant's (e.g., a moderator's) 16-character sessionToken and reuses it to impersonate that user within the conference. … |
| Remediation | Vendor-released patch: 3.0.21 - upgrade BigBlueButton to v3.0.21 or later, which replaces the insecure RandomStringUtils token generation with a java.security.SecureRandom-backed Util.randomAlphanumeric helper (fix commit 8457886c248aeba5597ee8749267602d6d117e98). … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, conduct a complete audit of BigBlueButton deployments to identify all systems running versions prior to 3.0.21, prioritizing instances that host sensitive or confidential communications. …
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