CVE-2026-49953

Summary

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.

Affected Software

Weaknesses

• CWE-804: Guessable CAPTCHA

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: yes
  • Technical Impact: partial

CVE Program Container

Additional References

• http://seclists.org/fulldisclosure/2026/Jun/4

References

• https://karmainsecurity.com/KIS-2026-10
• https://karmainsecurity.com/chaining-bugs-in-discuz-from-race-condition-to-rce
• https://www.vulncheck.com/advisories/discuz-x5-0-captcha-bypass-via-predictable-character-set

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