CVE-2026-49953 (GCVE-0-2026-49953)
Vulnerability from cvelistv5 – Published: 2026-06-15 18:45 – Updated: 2026-07-28 01:49 X_Open Source
VLAI
EPSS
VEX
Title
Discuz! X5.0 CAPTCHA Bypass via Predictable Character Set
Summary
Discuz! X5.0 releases 20260320 through 20260610 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.
Severity
6.5 (Medium)
SSVC
Exploitation: poc
Automatable: yes
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-06-15 22:04 UTC
CWE
- CWE-804 - Guessable CAPTCHA
Assigner
References
4 references
| URL | Tags |
|---|---|
| https://karmainsecurity.com/KIS-2026-10 | technical-description |
| https://karmainsecurity.com/chaining-bugs-in-disc… | exploit |
| https://www.vulncheck.com/advisories/discuz-x5-0-… | third-party-advisory |
| http://seclists.org/fulldisclosure/2026/Jun/4 |
Impacted products
1 product
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Discuz! | Discuz! X5.0 |
Affected:
20260320 , ≤ 20260610
(date)
cpe:2.3:a:discuz:discuzx:*:*:*:*:*:*:*:* |
Date Public
2026-06-13 00:00
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Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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Vulnerability timeline
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How durations are calculated
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
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They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.