Vulnerability in Discuz! X5.0
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.004 (29.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 30th percentile — 29.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.004 · change: -0.001
Affected products
- Discuz! X5.0 — versions 20260320
Weakness classification (CWE)
References
- karmainsecurity.com/KIS-2026-10 (technical-description)
- karmainsecurity.com/chaining-bugs-in-discuz-from-race-condition-to-rce (exploit)
- www.vulncheck.com/advisories/discuz-x5-0-captcha-bypass-via-predictable-charact… (third-party-advisory)
- af854a3a-2127-422b-91ae-364da2661108
Frequently asked questions
- What is CVE-2026-49953?
- CVE-2026-49953 is a medium-severity vulnerability in Discuz! X5.0, classified under CWE-804. CVSS score: 6.5/10. Published 2026-06-15.
- How severe is CVE-2026-49953?
- Medium severity. CVSS v3 base score is 6.5 out of 10.