CVE-2026-49953
Discuz! X5.0 CAPTCHA Bypass via Predictable Character Set
- State
- Published
- Severity
- 6.9 Medium
- Published
- Jun 15, 2026
- Updated
- Jul 28, 2026
- Reserved
- Jun 2, 2026
Description
Discuz! X5.0 releases 20260320 through 20260610 contains a CAPTCHA bypass vulnerability that allows unauthenticated remote attackers to defeat challenge controls by exploiting limited complexity and predictable character sets in generated CAPTCHA images. Attackers can train a custom optical character recognition model against collected CAPTCHA samples to reliably predict challenge text, bypassing protections on login, registration, and other functionality from automated abuse.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 6.9 Medium | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N | VulnCheck |
| 3.1 | 6.5 Medium | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N | VulnCheck |
Weaknesses
- CWE-804 Guessable CAPTCHA
Affected Products
| Product | Versions |
|---|---|
Discuz! X5.0Discuz! |
|
References
- https://karmainsecurity.com/KIS-2026-10technical-description
- https://karmainsecurity.com/chaining-bugs-in-discuz-from-race-condition-to-rceexploit
- https://www.vulncheck.com/advisories/discuz-x5-0-captcha-bypass-via-predictable-character-setthird-party-advisory
- http://seclists.org/fulldisclosure/2026/Jun/4
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