Automated CAPTCHA bypass via OCR-solvable challenges
Published Jun 15, 2026 · Updated Jun 15, 2026
Guessable CAPTCHA in Discuz! X5.0 releases 20260320 through 20260610 allows unauthenticated remote attackers to automate challenge solving via OCR. The image generator renders only four alphanumeric characters with limited complexity and predictable patterns, letting a trained CNN/LSTM/CTC model recognize samples at about 98% accuracy. The image challenge is enabled by default for registration and login; bypassing it removes the human-interaction barrier to automated registration, credential stuffing, and other protected workflows, but does not alone grant account access.
Summary
What happened
Guessable CAPTCHA in Discuz! X5.0 releases 20260320 through 20260610 allows unauthenticated remote attackers to automate challenge solving via OCR. The image generator renders only four alphanumeric characters with limited complexity and predictable patterns, letting a trained CNN/LSTM/CTC model recognize samples at about 98% accuracy. The image challenge is enabled by default for registration and login; bypassing it removes the human-interaction barrier to automated registration, credential stuffing, and other protected workflows, but does not alone grant account access.
The record
- CVE
- CVE-2026-49953
- Published
- Jun 15, 2026
- Updated
- Jun 15, 2026
- Vendor
- Comsenz
- Product
- Discuz! X
- Classifications
- CWE-804
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 15, 2026CVE publishedPublication date reported by the CVE source.
- Jun 15, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=20260320 <=20260610
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Discuz CAPTCHA bypass proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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