CVE-2026-49952

CRITICAL 9.1

Discuz! X5.0 Authentication Bypass via dbbak.php Encryption Oracle

CVSS Score

9.1

EPSS Score

0.0%

EPSS Percentile

0th

Discuz! X5.0 releases 20260320 through 20260501 contains an authentication bypass vulnerability that allows unauthenticated remote attackers to gain unauthorized access to database backup and restore functionality by exploiting a shared cryptographic key between UCenter integration and the database backup API exposed by dbbak.php. Attackers can inject a crafted payload through the username parameter during login to abuse the encryption oracle in logging_ctl::logging_more(), obtain a legitimately signed token, and use it to bypass authorization for database export and import operations, with the additional ability to trigger a race condition to impersonate arbitrary users.

CWE	CWE-323
Vendor	discuz!
Product	discuz! x5.0
Published	Jun 15, 2026
Last Updated	Jun 15, 2026

Stay Ahead of the Next One

Get instant alerts for discuz! discuz! x5.0

Be the first to know when new critical vulnerabilities affecting discuz! discuz! x5.0 are published — delivered to Slack, Telegram or Discord.

Get Free Alerts → Free · No credit card · 60 sec setup

CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Affected Versions

Discuz! / Discuz! X5.0

20260320 ≤ 20260501

References

NVD ↗ CVE.org ↗ EPSS Data ↗

karmainsecurity.com: https://karmainsecurity.com/KIS-2026-09 karmainsecurity.com: https://karmainsecurity.com/chaining-bugs-in-discuz-from-race-condition-to-rce gitee.com: https://gitee.com/Discuz/DiscuzX/commit/9962dad52c4c6999dabaf91ecd70377c680ff3c6 vulncheck.com: https://www.vulncheck.com/advisories/discuz-x5-0-authentication-bypass-via-dbbak-php-encryption-oracle

Credits

Egidio Romano