Vulnerability-Lookup

CVE-2026-93990 (GCVE-0-2026-93990)

Vulnerability from cvelistv5 – Published: 2026-09-19 22:58 – Updated: 2026-09-19 22:58

Title

Expat through 2.8.4 Malformed UTF-16 Acceptance via Unchecked Surrogate

Summary

Expat through 2.8.4 fails to validate low surrogates following high surrogates in UTF-16 input, allowing malformed UTF-16 sequences to be accepted. Attackers can craft UTF-16 encoded XML with lone high surrogates that consume following code units, hiding markup characters from the parser and enabling XML injection attacks.

Severity

8.7 (High)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CWE

CWE-176 - Improper Handling of Unicode Encoding

Assigner

VulnCheck mitre root

References

4 references

URL	Tags
https://github.com/libexpat/libexpat/pull/1282	issue-trackingpatch
https://github.com/libexpat/libexpat/commit/ff6e1…	patch
https://github.com/libexpat/libexpat	product
https://www.vulncheck.com/advisories/expat-throug…	third-party-advisory

Impacted products

1 product

Vendor	Product	Version	CPE status
libexpat	libexpat	Affected: 0 , ≤ 2.8.4 (semver) cpe:2.3:a:libexpat_project:libexpat::::::::

Date Public

2026-09-18 00:00

Credits

Kartik Kenchi (netliomax25-code)

Show details on NVD website

JSON

To clipboard

{
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      "affected": [
        {
          "defaultStatus": "unaffected",
          "packageURL": "pkg:github/libexpat/libexpat",
          "product": "libexpat",
          "repo": "https://github.com/libexpat/libexpat",
          "vendor": "libexpat",
          "versions": [
            {
              "lessThanOrEqual": "2.8.4",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:a:libexpat_project:libexpat:*:*:*:*:*:*:*:*",
                  "versionEndIncluding": "2.8.4",
                  "vulnerable": true
                }
              ],
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      "datePublic": "2026-09-18T00:00:00.000Z",
      "descriptions": [
        {
          "lang": "en",
          "value": "Expat through 2.8.4 fails to validate low surrogates following high surrogates in UTF-16 input, allowing malformed UTF-16 sequences to be accepted. Attackers can craft UTF-16 encoded XML with lone high surrogates that consume following code units, hiding markup characters from the parser and enabling XML injection attacks."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "NONE",
            "attackVector": "NETWORK",
            "baseScore": 8.7,
            "baseSeverity": "HIGH",
            "privilegesRequired": "NONE",
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            "subConfidentialityImpact": "NONE",
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            "userInteraction": "NONE",
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            "vulnIntegrityImpact": "HIGH"
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            "version": "3.1"
          },
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      "problemTypes": [
        {
          "descriptions": [
            {
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      "providerMetadata": {
        "dateUpdated": "2026-09-19T22:58:11.224Z",
        "orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
        "shortName": "VulnCheck"
      },
      "references": [
        {
          "name": "GitHub PR #1282",
          "tags": [
            "issue-tracking",
            "patch"
          ],
          "url": "https://github.com/libexpat/libexpat/pull/1282"
        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/libexpat/libexpat/commit/ff6e1d7e750bbe245178f51a47a965dc8342861a"
        },
        {
          "tags": [
            "product"
          ],
          "url": "https://github.com/libexpat/libexpat"
        },
        {
          "name": "VulnCheck Advisory: Expat through 2.8.4 Malformed UTF-16 Acceptance via Unchecked Surrogate",
          "tags": [
            "third-party-advisory"
          ],
          "url": "https://www.vulncheck.com/advisories/expat-through-2.8.4-malformed-utf-16-acceptance-via-unchecked-surrogate"
        }
      ],
      "title": "Expat through 2.8.4 Malformed UTF-16 Acceptance via Unchecked Surrogate",
      "x_generator": {
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      }
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  },
  "cveMetadata": {
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    "datePublished": "2026-09-19T22:58:11.224Z",
    "dateReserved": "2026-09-19T10:55:49.093Z",
    "dateUpdated": "2026-09-19T22:58:11.224Z",
    "state": "PUBLISHED"
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    "epss": {
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    "nvd": {
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                "defaultStatus": "unaffected",
                "packageURL": "pkg:github/libexpat/libexpat",
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                "repo": "https://github.com/libexpat/libexpat",
                "vendor": "libexpat",
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                    "lessThanOrEqual": "2.8.4",
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                    "version": "0",
                    "versionType": "semver"
                  }
                ]
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        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "Expat through 2.8.4 fails to validate low surrogates following high surrogates in UTF-16 input, allowing malformed UTF-16 sequences to be accepted. Attackers can craft UTF-16 encoded XML with lone high surrogates that consume following code units, hiding markup characters from the parser and enabling XML injection attacks."
          }
        ],
        "id": "CVE-2026-93990",
        "lastModified": "2026-09-19T23:17:10.203",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
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                "baseSeverity": "HIGH",
                "confidentialityImpact": "NONE",
                "integrityImpact": "HIGH",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
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              },
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          "cvssMetricV40": [
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                "Recovery": "NOT_DEFINED",
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                "attackRequirements": "NONE",
                "attackVector": "NETWORK",
                "availabilityRequirement": "NOT_DEFINED",
                "baseScore": 8.7,
                "baseSeverity": "HIGH",
                "confidentialityRequirement": "NOT_DEFINED",
                "exploitMaturity": "NOT_DEFINED",
                "integrityRequirement": "NOT_DEFINED",
                "modifiedAttackComplexity": "NOT_DEFINED",
                "modifiedAttackRequirements": "NOT_DEFINED",
                "modifiedAttackVector": "NOT_DEFINED",
                "modifiedPrivilegesRequired": "NOT_DEFINED",
                "modifiedSubAvailabilityImpact": "NOT_DEFINED",
                "modifiedSubConfidentialityImpact": "NOT_DEFINED",
                "modifiedSubIntegrityImpact": "NOT_DEFINED",
                "modifiedUserInteraction": "NOT_DEFINED",
                "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
                "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
                "modifiedVulnIntegrityImpact": "NOT_DEFINED",
                "privilegesRequired": "NONE",
                "providerUrgency": "NOT_DEFINED",
                "subAvailabilityImpact": "NONE",
                "subConfidentialityImpact": "NONE",
                "subIntegrityImpact": "NONE",
                "userInteraction": "NONE",
                "valueDensity": "NOT_DEFINED",
                "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
                "version": "4.0",
                "vulnAvailabilityImpact": "NONE",
                "vulnConfidentialityImpact": "NONE",
                "vulnIntegrityImpact": "HIGH",
                "vulnerabilityResponseEffort": "NOT_DEFINED"
              },
              "source": "disclosure@vulncheck.com",
              "type": "Secondary"
            }
          ]
        },
        "published": "2026-09-19T23:17:10.203",
        "references": [
          {
            "source": "disclosure@vulncheck.com",
            "url": "https://github.com/libexpat/libexpat"
          },
          {
            "source": "disclosure@vulncheck.com",
            "url": "https://github.com/libexpat/libexpat/commit/ff6e1d7e750bbe245178f51a47a965dc8342861a"
          },
          {
            "source": "disclosure@vulncheck.com",
            "url": "https://github.com/libexpat/libexpat/pull/1282"
          },
          {
            "source": "disclosure@vulncheck.com",
            "url": "https://www.vulncheck.com/advisories/expat-through-2.8.4-malformed-utf-16-acceptance-via-unchecked-surrogate"
          }
        ],
        "sourceIdentifier": "disclosure@vulncheck.com",
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    }
  }
}

GHSA-RFP9-FFQC-H4X8

Vulnerability from github – Published: 2026-09-20 00:30 – Updated: 2026-09-20 00:30

Details

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

8.7 (High)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Show details on source website

JSON

To clipboard

{
  "affected": [],
  "aliases": [
    "CVE-2026-93990"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-176"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-19T23:17:10Z",
    "severity": "HIGH"
  },
  "details": "Expat through 2.8.4 fails to validate low surrogates following high surrogates in UTF-16 input, allowing malformed UTF-16 sequences to be accepted. Attackers can craft UTF-16 encoded XML with lone high surrogates that consume following code units, hiding markup characters from the parser and enabling XML injection attacks.",
  "id": "GHSA-rfp9-ffqc-h4x8",
  "modified": "2026-09-20T00:30:23Z",
  "published": "2026-09-20T00:30:23Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-93990"
    },
    {
      "type": "WEB",
      "url": "https://github.com/libexpat/libexpat/pull/1282"
    },
    {
      "type": "WEB",
      "url": "https://github.com/libexpat/libexpat/commit/ff6e1d7e750bbe245178f51a47a965dc8342861a"
    },
    {
      "type": "WEB",
      "url": "https://github.com/libexpat/libexpat"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/expat-through-2.8.4-malformed-utf-16-acceptance-via-unchecked-surrogate"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

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 model, served locally by ML-Gateway. 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.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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.