CVE-2026-49953
CVE-2026-49953 is a medium-severity vulnerability with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-804.
Key facts
- Severity: Medium (CVSS 3.x base score 6.5)
- CVSS v4: 6.9
- EPSS exploit prediction: 0% (28th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-36793
- Weakness: CWE-804
- Published:
- Last modified:
Description
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.
Frequently asked questions
- What is CVE-2026-49953?
- 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.
- How severe is CVE-2026-49953?
- CVE-2026-49953 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.
- Is CVE-2026-49953 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (28th percentile), an estimate of the probability of exploitation in the next 30 days.
- How do I fix CVE-2026-49953?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- Does CVE-2026-49953 have an EU (EUVD) identifier?
- Yes. CVE-2026-49953 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-36793.
- When was CVE-2026-49953 published?
- CVE-2026-49953 was published on 2026-06-15 and last updated on 2026-06-17.
References
- https://karmainsecurity.com/KIS-2026-10
- https://karmainsecurity.com/chaining-bugs-in-discuz-from-race-condition-to-rce
- https://www.vulncheck.com/advisories/discuz-x5-0-captcha-bypass-via-predictable-character-set
- http://seclists.org/fulldisclosure/2026/Jun/4
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