CVE-2026-63476 (GCVE-0-2026-63476)

Vulnerability from cvelistv5 – Published: 2026-11-03 19:44 – Updated: 2026-11-03 19:44
VLAI
Title
isomorphic-git: Unbounded memory allocation from attacker-controlled delta target size (DoS)
Summary
isomorphic-git is a pure JavaScript implementation of Git for Node.js and browsers. Prior to 1.38.6, isomorphic-git reads a server-controlled targetSize while applying a packfile delta in src/utils/applyDelta.js and passes it without a bound to Buffer.alloc(targetSize). A malicious or man-in-the-middle-controlled remote can send one delta header that causes git.clone() or git.fetch() to allocate approximately 2 GB before validating the actual delta output. GitPackIndex.fromPack swallows the later size-mismatch error, so a host with sufficient memory may retain the resource waste without a visible failure, while containers, serverless functions, and small virtual machines may terminate. Node.js heap limits do not mitigate the off-heap Buffer allocation. This issue is fixed in version 1.38.6.
Severity
4.3 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L
CWE
  • CWE-400 - Uncontrolled Resource Consumption
  • CWE-789 - Memory Allocation with Excessive Size Value
Assigner
GitHub_M CNA under the mitre root
CNA scorecard C 72/100 over 7913 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
isomorphic-git isomorphic-git Affected: < 1.38.6
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "isomorphic-git",
          "vendor": "isomorphic-git",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 1.38.6"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "isomorphic-git is a pure JavaScript implementation of Git for Node.js and browsers. Prior to 1.38.6, isomorphic-git reads a server-controlled targetSize while applying a packfile delta in src/utils/applyDelta.js and passes it without a bound to Buffer.alloc(targetSize). A malicious or man-in-the-middle-controlled remote can send one delta header that causes git.clone() or git.fetch() to allocate approximately 2 GB before validating the actual delta output. GitPackIndex.fromPack swallows the later size-mismatch error, so a host with sufficient memory may retain the resource waste without a visible failure, while containers, serverless functions, and small virtual machines may terminate. Node.js heap limits do not mitigate the off-heap Buffer allocation. This issue is fixed in version 1.38.6."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "LOW",
            "baseScore": 4.3,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-400",
              "description": "CWE-400: Uncontrolled Resource Consumption",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-789",
              "description": "CWE-789: Memory Allocation with Excessive Size Value",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-11-03T19:44:06.908Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/isomorphic-git/isomorphic-git/security/advisories/GHSA-9x82-4j54-863h",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/isomorphic-git/isomorphic-git/security/advisories/GHSA-9x82-4j54-863h"
        },
        {
          "name": "https://github.com/isomorphic-git/isomorphic-git/pull/2370",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/isomorphic-git/isomorphic-git/pull/2370"
        },
        {
          "name": "https://github.com/isomorphic-git/isomorphic-git/commit/823843d1cd19182df79bc907c767f5bcecb39a0b",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/isomorphic-git/isomorphic-git/commit/823843d1cd19182df79bc907c767f5bcecb39a0b"
        },
        {
          "name": "https://github.com/isomorphic-git/isomorphic-git/releases/tag/v1.38.6",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/isomorphic-git/isomorphic-git/releases/tag/v1.38.6"
        }
      ],
      "source": {
        "advisory": "GHSA-9x82-4j54-863h",
        "discovery": "UNKNOWN"
      },
      "title": "isomorphic-git: Unbounded memory allocation from attacker-controlled delta target size (DoS)"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-63476",
    "datePublished": "2026-11-03T19:44:06.908Z",
    "dateReserved": "2026-07-16T21:37:45.769Z",
    "dateUpdated": "2026-11-03T19:44:06.908Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-63476",
      "date": "2026-11-04",
      "epss": "0.00285",
      "percentile": "0.21184"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "product": "isomorphic-git",
                "vendor": "isomorphic-git",
                "versions": [
                  {
                    "status": "affected",
                    "version": "\u003c 1.38.6"
                  }
                ]
              }
            ],
            "source": "security-advisories@github.com"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "isomorphic-git is a pure JavaScript implementation of Git for Node.js and browsers. Prior to 1.38.6, isomorphic-git reads a server-controlled targetSize while applying a packfile delta in src/utils/applyDelta.js and passes it without a bound to Buffer.alloc(targetSize). A malicious or man-in-the-middle-controlled remote can send one delta header that causes git.clone() or git.fetch() to allocate approximately 2 GB before validating the actual delta output. GitPackIndex.fromPack swallows the later size-mismatch error, so a host with sufficient memory may retain the resource waste without a visible failure, while containers, serverless functions, and small virtual machines may terminate. Node.js heap limits do not mitigate the off-heap Buffer allocation. This issue is fixed in version 1.38.6."
          }
        ],
        "id": "CVE-2026-63476",
        "lastModified": "2026-11-03T20:18:16.200",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "LOW",
                "baseScore": 4.3,
                "baseSeverity": "MEDIUM",
                "confidentialityImpact": "NONE",
                "integrityImpact": "NONE",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "REQUIRED",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L",
                "version": "3.1"
              },
              "exploitabilityScore": 2.8,
              "impactScore": 1.4,
              "source": "security-advisories@github.com",
              "type": "Secondary"
            }
          ]
        },
        "published": "2026-11-03T20:18:16.063",
        "references": [
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/isomorphic-git/isomorphic-git/commit/823843d1cd19182df79bc907c767f5bcecb39a0b"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/isomorphic-git/isomorphic-git/pull/2370"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/isomorphic-git/isomorphic-git/releases/tag/v1.38.6"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/isomorphic-git/isomorphic-git/security/advisories/GHSA-9x82-4j54-863h"
          }
        ],
        "sourceIdentifier": "security-advisories@github.com",
        "vulnStatus": "Deferred",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-400"
              },
              {
                "lang": "en",
                "value": "CWE-789"
              }
            ],
            "source": "security-advisories@github.com",
            "type": "Primary"
          }
        ]
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-11-03T21:08:27+00:00",
      "cve": "CVE-2026-63476",
      "id": "CVE-2026-63476",
      "initial_release_date": "2026-11-03T19:44:06.908000+00:00",
      "product_status:known_affected": "6",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "isomorphic-git: isomorphic-git: Denial of Service via unbounded memory allocation during packfile processing",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63476.json",
      "version": "3"
    }
  }
}



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