Auth bypass in Mlogclub Bbs-Go
CVE-2026-111639
bbs-go through 4.4.6 contains an authentication bypass vulnerability in the /api/login/google_one_tap endpoint that allows remote attackers to log in as other users by submitting Google ID tokens issued to any OAuth client. Attackers operating their own Google OAuth client can capture a victim's Google-signed ID token and replay it, since the aud claim is never checked, to obtain an authenticated session as the victim's Google-linked account.
Vulnerability class: Broken Authentication
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
Weakness classification (CWE)
References
- hackmd.io/@hieuPenguinnn/bbs-go-google-one-tap-id-token-audience-confusion-acco… (third-party-advisory)
- github.com/mlogclub/bbs-go/blob/v4.4.6/internal/pkg/google/jwt.go (technical-description)
- github.com/mlogclub/bbs-go/blob/v4.4.6/internal/services/third_user_service.go (technical-description)
- www.vulncheck.com/advisories/bbs-go-through-4.4.6-account-takeover-via-google-o… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-111639?
- CVE-2026-111639 is a high-severity vulnerability in Mlogclub Bbs-Go, classified under Improper Authentication. CVSS score: 8.1/10. Published 2026-10-16.
- How severe is CVE-2026-111639?
- High severity. CVSS v3 base score is 8.1 out of 10.