WWBN/AVideo has CAPTCHA Bypass via Attacker-Controlled Length Parameter and Missing Token Invalidation on Failure

published 2026-04-14 6 mo ago modified 2026-10-26 13 d ago also GHSA-hg7g-56h5-5pqr , EUVD-2026-24527

cvss: 5.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 12%
public exploits: 0; none known

WWBN AVideo is an open source video platform. In versions 29.0 and prior, `objects/getCaptcha.php` accepts the CAPTCHA length (`ql`) directly from the query string with no clamping or sanitization, letting any unauthenticated client force the server to generate a 1-character CAPTCHA word. Combined with a case-insensitive `strcasecmp` comparison over a ~33-character alphabet and the fact that failed validations do NOT consume the stored session token, an attacker can trivially brute-force the CAPTCHA on any endpoint that relies on `Captcha::validation()` (user registration, password recovery, contact form, etc.) in at most ~33 requests per session. Commit bf1c76989e6a9054be4f0eb009d68f0f2464b453 contains a fix.

Patch / fix

links 1

github.com/WWBN/AVideo@bf1c769 commit

CISA SSVC

Exploitation: Proof of concept is public
Automatable: yes
Technical impact: partial
Assessed: 6 mo ago (2026-04-22)

Exploit prediction

0.22% chance of exploitation in the next 30 days, higher than 12% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/WWBN/AVideo/security/advisories/GHSA-hg7g-56h5-5pqr referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	3.1	5.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
GitHub	3.1	5.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
packagist	wwbn/avideo	<=29.0	no fix listed

Affected products

WWBN AVideo

Classification

Weakness

CWE-804 Guessable CAPTCHA

References

github.com /WWBN/AVideo/commit/bf1c76989e6a9054be4f0eb009d68f0f2464b453
web, patch
github.com /WWBN/AVideo/security/advisories/GHSA-hg7g-56h5-5pqr
exploit, web, mitigation, vendor-advisory
nvd.nist.gov /vuln/detail/CVE-2026-40935
advisory
github.com /WWBN/AVideo
package

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary