EUVD-2026-36793
GHSA-p3qj-vw7q-v9pc
Severity by source
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Network-accessible unauthenticated bypass (AV:N/PR:N/AC:L) with limited confidentiality and integrity impact on protected endpoints; no availability impact and scope unchanged.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
1DescriptionCVE.org
Discuz! X5.0 releases 20260320 through 20260501 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.
AnalysisAI
CAPTCHA challenge controls in Discuz! X5.0 (releases 20260320-20260501) can be reliably defeated by unauthenticated remote attackers who harvest samples from exposed forum endpoints and train a custom optical character recognition model to predict challenge text. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | No special conditions are required for the CAPTCHA bypass itself - any internet-facing Discuz! … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N) scores 6.9 Medium, reflecting network-accessible, zero-prerequisite exploitation with low individual-impact ceiling. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker sends thousands of unauthenticated GET requests to the Discuz! X5.0 forum's CAPTCHA endpoint, collecting labeled image samples which are used to train a lightweight CNN-based OCR model achieving high solve accuracy against unseen challenges. … |
| Remediation | No exact patched release version is confirmed in the available input data; operators must verify directly with the Discuz! … Detailed patch versions, workarounds, and compensating controls in full report. |
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External POC / Exploit Code
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