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Medium

Dulwich has unbounded memory allocation in receive-pack from crafted thin packs

Type: advisorySources: OSV

Dulwich is a pure-Python implementation of the Git file formats and protocols. Starting in version 0.1.0 and prior to version 1.2.5, a client with push access could push a tiny crafted thin pack (~174 bytes) whose delta header declares a huge dest_size. When dulwich ingested it via add_thin_pack / apply_delta, it would allocate hundreds of MB of memory based on that attacker-controlled size, with no relationship to the actual bytes received. Operators running a Dulwich-based Git server that exposes git-receive-pack (i.e. accepts pushes) - for example via dulwich.server functionality, the HTTP smart server, or anything built on ReceivePackHandler - are impacted. The issue is patched in 1.2.5. add_thin_pack now accepts a max_input_size keyword (bytes; 0/None = unlimited, matching git's semantics), and ReceivePackHandler reads receive.maxInputSize from the repository config and passes it through. Wire reads are counted and a PackInputTooLarge exception is raised once the cap is exceeded - equivalent to git index-pack --max-input-size. Users should upgrade to Dulwich 1.2.5 or later and set receive.maxInputSize in their server's repository config to a sane bound for their environment. On unpatched versions, receive.maxInputSize has no effect, so it cannot be used as a workaround. Until upgrading, operators should restrict dulwich-receive-pack (push) access to trusted, authenticated clients only, or disable it entirely on servers that only need to serve fetches and/or run the serve

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-47734
Confirmed fixed CVEs
Not specified
Updated in this feed
7 Nov 2026, 06:11 UTC · Revision 1

Source evidence

Dulwich has unbounded memory allocation in receive-pack from crafted thin packs

core-osv · Original source

Published 10 Jun 2026, 22:11 UTC

Dulwich is a pure-Python implementation of the Git file formats and protocols. Starting in version 0.1.0 and prior to version 1.2.5, a client with push access could push a tiny crafted thin pack (~174 bytes) whose delta header declares a huge dest_size. When dulwich ingested it via add_thin_pack / apply_delta, it would allocate hundreds of MB of memory based on that attacker-controlled size, with no relationship to the actual bytes received. Operators running a Dulwich-based Git server that exposes git-receive-pack (i.e. accepts pushes) - for example via dulwich.server functionality, the HTTP smart server, or anything built on ReceivePackHandler - are impacted. The issue is patched in 1.2.5. add_thin_pack now accepts a max_input_size keyword (bytes; 0/None = unlimited, matching git's semantics), and ReceivePackHandler reads receive.maxInputSize from the repository config and passes it through. Wire reads are counted and a PackInputTooLarge exception is raised once the cap is exceeded - equivalent to git index-pack --max-input-size. Users should upgrade to Dulwich 1.2.5 or later and set receive.maxInputSize in their server's repository config to a sane bound for their environment. On unpatched versions, receive.maxInputSize has no effect, so it cannot be used as a workaround. Until upgrading, operators should restrict dulwich-receive-pack (push) access to trusted, authenticated clients only, or disable it entirely on servers that only need to serve fetches and/or run the serve

osv:CVE-2026-47734
Complete source record
{
  "id": "262658e41ede401e4a28083ab5fdc8d1618b6f2663450c507e5ee009fc649579",
  "url": "https://osv.dev/vulnerability/CVE-2026-47734",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Dulwich has unbounded memory allocation in receive-pack from crafted thin packs",
    "summary": "Dulwich is a pure-Python implementation of the Git file formats and protocols. Starting in version 0.1.0 and prior to version 1.2.5, a client with push access could push a tiny crafted thin pack (~174 bytes) whose delta header declares a huge dest_size. When dulwich ingested it via add_thin_pack / apply_delta, it would allocate hundreds of MB of memory based on that attacker-controlled size, with no relationship to the actual bytes received. Operators running a Dulwich-based Git server that exposes git-receive-pack (i.e. accepts pushes) - for example via dulwich.server functionality, the HTTP smart server, or anything built on ReceivePackHandler - are impacted. The issue is patched in 1.2.5. add_thin_pack now accepts a max_input_size keyword (bytes; 0/None = unlimited, matching git's semantics), and ReceivePackHandler reads receive.maxInputSize from the repository config and passes it through. Wire reads are counted and a PackInputTooLarge exception is raised once the cap is exceeded - equivalent to git index-pack --max-input-size. Users should upgrade to Dulwich 1.2.5 or later and set receive.maxInputSize in their server's repository config to a sane bound for their environment. On unpatched versions, receive.maxInputSize has no effect, so it cannot be used as a workaround. Until upgrading, operators should restrict dulwich-receive-pack (push) access to trusted, authenticated clients only, or disable it entirely on servers that only need to serve fetches and/or run the serve",
    "evidence": "osv:CVE-2026-47734",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-47734",
      "aliases": [
        "CVE-2026-47734",
        "GHSA-xrvj-v92f-53gj",
        "PYSEC-2026-2466"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/jelmer/dulwich",
              "type": "GIT",
              "events": [
                {
                  "introduced": "bd0bc8c85b439d0824363c12701fccb992b203dd"
                },
                {
                  "fixed": "073f4dfa9840af2da59887ed828b026b609faa6c"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0.1.0"
                      },
                      {
                        "fixed": "1.2.5"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "073f4dfa9840af2da59887ed828b026b609faa6c"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "dulwich-1.2.5"
                  }
                ]
              }
            }
          ],
          "versions": [
            "dulwich-1.2.4",
            "dulwich-1.2.3",
            "dulwich-1.2.2",
            "dulwich-1.2.1",
            "dulwich-1.2.0",
            "dulwich-1.1.0",
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            "dulwich-0.25.2",
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            "dulwich-0.24.8",
            "dulwich-0.24.7",
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            "dulwich-0.24.5",
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            "dulwich-0.24.1",
            "dulwich-0.24.0",
            "dulwich-0.23.2",
            "dulwich-0.23.1",
            "dulwich-0.22.8",
            "dulwich-0.22.7",
            "dulwich-0.22.6",
            "dulwich-0.22.5",
            "dulwich-0.22.4",
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            "dulwich-0.22.2",
            "dulwich-0.22.1",
            "dulwich-0.22.0",
            "dulwich-0.21.7",
            "dulwich-0.21.6",
            "dulwich-0.21.5",
            "dulwich-0.21.4.1",
            "dulwich-0.21.3",
            "dulwich-0.21.2",
            "dulwich-0.21.1",
            "dulwich-0.21.0",
            "dulwich-0.20.50",
            "dulwich-0.20.44",
            "dulwich-0.20.43",
            "dulwich-0.20.42",
            "dulwich-0.20.41",
            "dulwich-0.20.40",
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            "dulwich-0.20.14",
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            "dulwich-0.20.12",
            "dulwich-0.20.11",
            "dulwich-0.20.9",
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            "dulwich-0.20.7",
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            "dulwich-0.20.5",
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            "dulwich-0.20.1",
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            "dulwich-0.17.0",
            "dulwich-0.16.3",
            "dulwich-0.16.2",
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            "dulwich-0.5.0",
            "dulwich-0.4.1",
            "dulwich-0.4.0",
            "dulwich-0.3.3",
            "dulwich-0.3.2",
            "dulwich-0.3.1",
            "dulwich-0.3.0",
            "dulwich-0.2.1",
            "dulwich-0.2.0",
            "dulwich-0.1.1",
            "dulwich-0.1.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-47734.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:50.059444226Z",
      "provider": "osv",
      "references": [
        "https://github.com/jelmer/dulwich/releases/tag/dulwich-1.2.5",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/47xxx/CVE-2026-47734.json",
        "https://github.com/jelmer/dulwich/security/advisories/GHSA-xrvj-v92f-53gj",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-47734"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-400",
          "CWE-789"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/47xxx/CVE-2026-47734.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-47734",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 518446,
  "published_at": "2026-06-10T22:11:02.704+00:00"
}