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CVE-2017-8923

Status: ModifiedCritical (9.8)—

The zend_string_extend function in Zend/zend_string.h in PHP through 7.1.5 does not prevent changes to string objects that result in a negative length, which allows remote attackers to cause a denial of service (application crash) or possibly have unspecified other impact by leveraging a script's use of .= with a long string.

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)

PHP — PHP

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2017-8923",
  "cveTags": [],
  "metrics": {
    "cvssMetricV2": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "version": "2.0",
          "baseScore": 7.5,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:L/Au:N/C:P/I:P/A:P",
          "authentication": "NONE",
          "integrityImpact": "PARTIAL",
          "accessComplexity": "LOW",
          "availabilityImpact": "PARTIAL",
          "confidentialityImpact": "PARTIAL"
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        "acInsufInfo": false,
        "impactScore": 6.4,
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        "obtainAllPrivilege": false,
        "exploitabilityScore": 10,
        "obtainUserPrivilege": false,
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    "cvssMetricV31": [
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          "attackVector": "NETWORK",
          "baseSeverity": "CRITICAL",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
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        "impactScore": 5.9,
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  "affected": [
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      "affectedData": [
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  "published": "2017-05-12T20:29:00.500",
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      "url": "http://www.securityfocus.com/bid/98518",
      "tags": [
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      "source": "cve@mitre.org"
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      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://bugs.php.net/bug.php?id=74577",
      "tags": [
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        "Issue Tracking",
        "Vendor Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://security.netapp.com/advisory/ntap-20241227-0007/",
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    }
  ],
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "CWE-787"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "The zend_string_extend function in Zend/zend_string.h in PHP through 7.1.5 does not prevent changes to string objects that result in a negative length, which allows remote attackers to cause a denial of service (application crash) or possibly have unspecified other impact by leveraging a script's use of .= with a long string."
    },
    {
      "lang": "es",
      "value": "La función zend_string_extend en el archivo Zend/zend_string.h en PHP hasta de la versión 7.1.5 no impide cambios en los objetos de cadena que resultan en una longitud negativa, lo que permite a los atacantes remotos causar una denegación de servicio (bloqueo de aplicación) o posiblemente tener otro impacto no especificado  explotando el uso de scripts .= con una cadena larga."
    }
  ],
  "lastModified": "2026-06-17T01:27:12.450",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
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  "sourceIdentifier": "cve@mitre.org"
}