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PatchSiren cyber security CVE debrief

CVE-2026-49953 Discuz! CVE debrief

CVE-2026-49953 is a CAPTCHA bypass vulnerability in Discuz! X5.0 releases from 20260320 to 20260610. The vulnerability allows unauthenticated remote attackers to bypass challenge controls by exploiting the 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.

Vendor
Discuz!
Product
Discuz! X5.0
CVSS
MEDIUM 6.9
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-15
Original CVE updated
2026-06-16
Advisory published
2026-06-15
Advisory updated
2026-06-16

Who should care

Users of Discuz! X5.0 releases from 20260320 to 20260610 should apply patches or mitigations to prevent CAPTCHA bypass attacks.

Technical summary

The vulnerability has a CVSS score of 6.9 and is classified as MEDIUM severity. The CVSS vector is 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.

Defensive priority

MEDIUM

Recommended defensive actions

  • Apply patches or updates to Discuz! X5.0 releases from 20260320 to 20260610.
  • Implement additional security measures to prevent automated abuse, such as IP blocking or rate limiting.

Evidence notes

The vulnerability was reported by Karmainsecurity and is tracked under CVE-2026-49953.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-49953 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-49953

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-49953 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-49953

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.