CVE-2026-49953 (CVSS 6.5)

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.

Is your site exposed to CVE-2026-49953?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

6.5

MEDIUM

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

EPSS — Exploit Prediction

0.0036

Probability of exploitation

0.28%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-804 CWE-804

References

Other 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

Frequently Asked Questions

What is 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. It has a CVSS v3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2026-49953? +

CVE-2026-49953 has a CVSS v3.1 score of 6.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0036, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-49953? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2026-112067

The extension hides the correct answer to each CAPTCHA inside the image data of the CAPTCHA itself. Anyone who can …

CVE-2025-40916 9.1

Mojolicious::Plugin::CaptchaPNG version 1.05 for Perl uses a weak random number source for generating the captcha. That version uses the built-in …

CVE-2025-50850 8.6

An issue was discovered in CS Cart 4.18.3 allows the vendor login functionality lacks essential security controls such as CAPTCHA …

CVE-2024-23566 6.5

HCL Aftermarket EPC is vulnerable to brute force attacks since application doesn’t have captcha implemented. It can lead to various …

CVE-2026-127206 5.3

Image CAPTCHA for Contact Form 7 and WPForms through 3.3.29 contains a CAPTCHA bypass vulnerability that allows unauthenticated attackers to …

CVE-2025-1262 5.3

The Advanced Google reCaptcha plugin for WordPress is vulnerable to CAPTCHA Bypass in versions up to, and including, 1.27 . …

CVE-2026-49953