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CVE-2021-21317

Status: ModifiedMedium (5.3)—

uap-core in an open-source npm package which contains the core of BrowserScope's original user agent string parser. In uap-core before version 0.11.0, some regexes are vulnerable to regular expression denial of service (REDoS) due to overlapping capture groups. This allows remote attackers to overload a server by setting the User-Agent header in an HTTP(S) request to maliciously crafted long strings. This is fixed in version 0.11.0. Downstream packages such as uap-python, uap-ruby etc which depend upon uap-core follow different version schemes.

CVSS

Exploitation probability (EPSS)

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

Affected technologies (1)

Uap-core Project — Uap-core

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2021-21317",
  "cveTags": [],
  "metrics": {
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        "source": "nvd@nist.gov",
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          "baseScore": 5,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:L/Au:N/C:N/I:N/A:P",
          "authentication": "NONE",
          "integrityImpact": "NONE",
          "accessComplexity": "LOW",
          "availabilityImpact": "PARTIAL",
          "confidentialityImpact": "NONE"
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        "acInsufInfo": false,
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        "obtainUserPrivilege": false,
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          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
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          "privilegesRequired": "NONE",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 1.4,
        "exploitabilityScore": 3.9
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        "type": "Primary",
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  "published": "2021-02-16T18:15:12.583",
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  "vulnStatus": "Modified",
  "weaknesses": [
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      "description": [
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          "value": "CWE-400"
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      "description": [
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          "lang": "en",
          "value": "CWE-1333"
        }
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  "descriptions": [
    {
      "lang": "en",
      "value": "uap-core in an open-source npm package which contains the core of BrowserScope's original user agent string parser. In uap-core before version 0.11.0, some regexes are vulnerable to regular expression denial of service (REDoS) due to overlapping capture groups. This allows remote attackers to overload a server by setting the User-Agent header in an HTTP(S) request to maliciously crafted long strings. This is fixed in version 0.11.0. Downstream packages such as uap-python, uap-ruby etc which depend upon uap-core follow different version schemes."
    },
    {
      "lang": "es",
      "value": "uap-core en un paquete npm de código abierto que contiene el core del analizador de cadenas del agente de usuario original de BrowserScope.&#xa0;En uap-core versiones anteriores a 0.11.0, algunas expresiones regulares son vulnerables a una denegación de servicio de expresión regular (REDoS) debido a la superposición de grupos de captura.&#xa0;Esto permite a atacantes remotos sobrecargar un servidor configurando el encabezado User-Agent en una petición HTTP(S) en cadenas largas diseñadas maliciosamente.&#xa0;Esto es corregido en versión 0.11.0.&#xa0;Los paquetes posteriores como uap-python, uap-ruby, etc., que dependen de uap-core, siguen esquemas de versiones diferentes"
    }
  ],
  "lastModified": "2026-06-17T03:35:17.093",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
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}