CVE-2026-49953

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.

CVSS 4.0

6.9CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

CVSS 3.1

6.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS

0.4% chance of exploitation in the next 30 days; higher than 29% of CVEs (scores of 2026-10-25)

CWE

CWE-804

Published

2026-06-15

Modified

2026-10-25

Record from

the NVD, synced 2026-10-25

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

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