CVE-2021-47876
Published: 21 January 2026
Summary
CVE-2021-47876 is a medium-severity Allocation of Resources Without Limits or Throttling (CWE-770) vulnerability in Geogebra (inferred from references). Its CVSS base score is 6.7 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 26.3th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified are NIST 800-53 SC-5 (Denial-of-service Protection) and SI-10 (Information Input Validation).
Deeper analysis
CVE-2021-47876 is a denial-of-service vulnerability in GeoGebra Classic version 5.0.631.0-d, specifically affecting the 'Entrada:' input field. The flaw, tied to CWE-770 (Allocation of Resources Without Limits or Throttling), allows attackers to crash the application by providing oversized buffer content, such as a large string of 800,000 repeated characters pasted into the field. The vulnerability carries a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H), indicating high-impact availability disruption without confidentiality or integrity effects.
The vulnerability is exploitable by unauthenticated remote attackers with low complexity and no user interaction required. An attacker can generate the oversized buffer and deliver it to the input field, triggering an application crash and rendering GeoGebra Classic unavailable to the targeted user. This enables denial-of-service attacks against individuals or systems running the affected version.
Advisories from VulnCheck (https://www.vulncheck.com/advisories/geogebra-classic-d-denial-of-service) and an Exploit-DB proof-of-concept (https://www.exploit-db.com/exploits/49654) detail the issue, with the official GeoGebra site (https://www.geogebra.org) serving as a resource for updates. Practitioners should consult these for patch availability or workarounds, such as input validation or upgrading to a fixed version.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-3628
Vulnerability details
GeoGebra Classic 5.0.631.0-d contains a denial of service vulnerability in the input field that allows attackers to crash the application by sending oversized buffer content. Attackers can generate a large buffer of 800,000 repeated characters and paste it into the…
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'Entrada:' input field to trigger an application crash.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
CVE enables direct exploitation of an input-handling flaw (oversized buffer) to crash the endpoint application, matching T1499.004 Application or System Exploitation for Endpoint DoS.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly mitigates the vulnerability by validating input length and content in fields like 'Entrada:' to reject oversized buffers exceeding safe limits.
Provides comprehensive denial-of-service protection mechanisms such as resource throttling and limits to counter oversized input attacks causing application crashes.
Enforces strict information input restrictions, including maximum character lengths, at application boundaries to block excessively large strings from crashing the input field.