Vulnerability · Published Jun 15, 2026 · Assigned by VulnCheck
CVE-2026-49952Discuz! X5.0 Authentication Bypass via dbbak.php Encryption Oracle
Critical 9.1
In plain English
A critical-severity security flaw in Discuz! X5.0 from Discuz!. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 4.7% (higher than 92% of all known vulnerabilities). Ready-made attack tooling exists: Nuclei, public proof-of-concept code.
Official description
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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Discuz! | Discuz! X5.0 | 20260320 – through 20260501 |
Weakness: CWE-323 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
References
- https://karmainsecurity.com/KIS-2026-09 technical-description
- https://karmainsecurity.com/chaining-bugs-in-discuz-from-race-condition-to-rce exploit
- https://gitee.com/Discuz/DiscuzX/commit/9962dad52c4c6999dabaf91ecd70377c680ff3c6 patch
- https://www.vulncheck.com/advisories/discuz-x5-0-authentication-bypass-via-dbbak-php-encryption-oracle third-party-advisory
- http://seclists.org/fulldisclosure/2026/Jun/3