CVE-2026-49953

medium

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.

References

https://www.vulncheck.com/advisories/discuz-x5-0-captcha-bypass-via-predictable-character-set

https://karmainsecurity.com/chaining-bugs-in-discuz-from-race-condition-to-rce

https://karmainsecurity.com/KIS-2026-10

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

Details

Source: Mitre, NVD

Published: 2026-06-15

Updated: 2026-06-16

Risk Information

CVSS v2

Base Score: 6.4

Vector: CVSS2#AV:N/AC:L/Au:N/C:P/I:P/A:N

Severity: Medium

CVSS v3

Base Score: 6.5

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

Severity: Medium

CVSS v4

Base Score: 6.9

Vector: 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

Severity: Medium

EPSS

EPSS: 0.00359