CAPTCHA bypass via attacker-controlled challenge length
Published Apr 21, 2026 · Updated Apr 21, 2026
Guessable CAPTCHA in World Wide Broadcast Network AVideo 29.0 and earlier allows remote attackers to bypass anti-bot checks. objects/getCaptcha.php accepts the ql query value without validation or clamping, so it stores a one-character challenge; Captcha::validation() compares guesses case-insensitively and preserves the session token after failed attempts. Unauthenticated access to a CAPTCHA-protected endpoint is sufficient to exhaust the 33-value keyspace, enabling automated registration, recovery-message spam, and other endpoint abuse without directly disclosing data or granting privileges.
Summary
What happened
Guessable CAPTCHA in World Wide Broadcast Network AVideo 29.0 and earlier allows remote attackers to bypass anti-bot checks. objects/getCaptcha.php accepts the ql query value without validation or clamping, so it stores a one-character challenge; Captcha::validation() compares guesses case-insensitively and preserves the session token after failed attempts. Unauthenticated access to a CAPTCHA-protected endpoint is sufficient to exhaust the 33-value keyspace, enabling automated registration, recovery-message spam, and other endpoint abuse without directly disclosing data or granting privileges.
The record
- CVE
- CVE-2026-40935
- Published
- Apr 21, 2026
- Updated
- Apr 21, 2026
- Vendor
- World Wide Broadcast Network
- Product
- AVideo
- Classifications
- CWE-804
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 21, 2026CVE publishedPublication date reported by the CVE source.
- Apr 21, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=<= 29.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
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
- GHSA 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
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo